The Gulf, Mobile, and Ohio Passenger Terminal in Mobile, Alabama, which has Spanish influences with its cream walls and red clay tiles, was designed by P. Thornton Marye. It was completed in 1907 and has undergone restoration since passenger train service ceased in the 1950s.

The University of Alaska Museum of the North is home to numerous exhibits showcasing the native cultures, natural wonders, and wildlife of our nation's largest state. It's also a stylish refuge from the cold.

The Chapel of the Holy Cross in Sedona was completed in 1956, and it juts majestically from a red stone butte, some 200 feet above the ground.

The beautiful Thorncrown Chapel in Eureka Springs looks like an open-air structure, but it's actually a serene, glass-enclosed architectural marvel.

It was designed in 1960, but the Chemosphere still looks futuristic. It's a house with 2,200 square feet of space, perched atop a 30-foot concrete pole. And it's survived every major Californian earthquake in the San Fernando Valley since it was built.

Mesa Verde National Park, a UNESCO World Heritage Site, features some of the best-preserved prehistoric landscapes of the Ancestral Puebloan people. These ancient dwellings, where the Ancestral Puebloans once lived, were constructed on the sides of natural cliffs.

While most dwellings had only one to five rooms, the Cliff Palace, the largest known cliff dwelling in North America, had 150 rooms, 23 sacred meeting spaces, and housed about 100 people, according to the National Park Service.

The main feature of Grace Farms in New Canaan is a serpentine wooden pavilion that links glass-walled rooms, including a library, stage, tea room, and a gym with a full basketball court. Completed in 2015, it's open to the public for free.

The country's oldest state has some classic buildings that stand the test of time. Wilmington's Grand Opera House, built in 1871, is as classic as it gets.

The Salvador Dalí Museum in St. Petersburg is a fittingly unique tribute to the beloved master of surrealism. The museum boasts the largest collection of Dalí's work outside Europe.

This might not look much like other buildings in this list, but the Ocmulgee Mounds National Park's Earth Lodge dates back to the year 1015, per the National Park Service.

The lodge is a reconstructed council chamber of the native Mississippian culture. While the walls and ceiling were reconstructed in the late 1930s, the clay floor remains the same as the original, dating back over a thousand years.

ʻIolani Palace in Honolulu is the only royal palace on United States soil. David Kalākaua, the last reigning king of Hawaii and the first monarch to travel around the world, was inspired by the European palaces he saw during his 1881 voyage.

The Dog Bark Park Inn in Cottonwood is a delightful piece of American kitsch. The bed and breakfast is shaped like two charming beagles.

Although there are between 5 and 6 million adherents to the Bahá'í Faith, there are only eight continental houses of worship worldwide. The one in Wilmette, Illinois, is the oldest still standing, and the only one in the United States.

When the West Baden Springs Hotel opened in 1902, it was billed as the Eighth Wonder of the World. While enjoying the view from inside the massive domed atrium — at one point the largest in the world — it's easy to see why.

Father Paul Dobberstein promised to build a shrine to the Virgin Mary as she helped cure his grave case of pneumonia. His resulting Grotto of the Redemption in West Bend is made of rocks, shells, fossils, and gems pressed into concrete. It's the size of a football field.

The Big Well in Greensburg is a museum that rests atop its titular main attraction: the largest hand-dug well in the world, spanning 32 feet in diameter and reaching a depth of 109 feet.

Churchill Downs, most famously the host of the Kentucky Derby, can hold 120,000 excited, sometimes rowdy, racing fans at max capacity.

The Pontalba Buildings, which make up two sides of New Orleans' Jackson Square, are emblematic of the French Quarter. Some of the residences on the upper floors are believed to be the oldest continuously rented apartments in the country.

The Portland Head Light — one of the state's many lighthouses — has been around since 1791. It was built under the directive of George Washington himself.

The American Visionary Art Museum in Baltimore showcases outsider art. All the works within its wonky exterior were made by inspired, self-taught creators.

Simmons Hall at MIT is the coolest dorm building in the US. It looks like a monstrous Tetris piece combined with underground caverns.

The museum, one of the oldest and largest dedicated to African American history, is a three-story building designed with influences of African and local Detroit architecture. The building features a stunning 55-foot-tall glass dome ceiling.

The Marjorie McNeely Conservatory at Saint Paul's Como Park was opened to the public in 1915 and features Japanese, Bonsai, and butterfly gardens, among others.

Designed by Frank Gehry — whose striking work also includes the Louis Vuitton Foundation in Paris, the Walt Disney Concert Hall in Los Angeles, and the Guggenheim Museum Bilbao in Spain — the curved metal pods, which house pottery at Biloxi's Ohr-O'Keefe Museum of Art, are meant to look as if they were "dancing with the trees," per the museum's website.

The parking garage at the Kansas City Library is called the Community Bookshelf. It displays the giant spines of 22 classic books that were suggested by Kansas City readers.

Construction started on the Montana State Capitol in 1896. The inside of the rotunda salutes four types of people central to the state's early history: a native American, an explorer, a gold miner, and a cowboy.

The Nebraska Capitol in Lincoln is one of the greatest state capitol buildings in the US. Built between 1922 and 1932, the building features artworks representing the development of law and the state of Nebraska.

The distinctive beehive-shaped Ward Charcoal Ovens in Ely were built for silver mining back in the 1870s, and they still look like nothing else on the landscape.

Built in 1902, the Mount Washington Hotel — today operating as the Omni Mount Washington Resort — is one of the last remaining grand hotels in the state, and is rumored to be haunted.

Nassau Hall is the oldest building at Princeton University, dating back to the 1750s. While it now houses the school's administrative offices, during the Revolutionary War it was occupied by both British and American forces and suffered damage during the battles.

Hundreds of years old, the Taos Pueblo is a multi-story complex built by Native Americans from the region. It looks like one big, molded piece, and it's still used as a residence.

The Empire State Building gets all the hype, but it's the Chrysler Building that's really the most magnificent skyscraper in New York City. The Art Deco-style building was the tallest in the world when it was built, but it was beaten out by — you guessed it — the Empire State Building just 11 months later.

Give it to North Carolina for having its most beautiful building designated as a civil landmark. The state's Executive Mansion in Raleigh is the home of the governor and a high-profile event venue that's open to public tours.

At the center of the North Dakota Heritage Center in Bismarck is a great glass cube flanked by two copper-colored wings. It's the home of the state's greatest treasures, including Native American historical artifacts and lots of dinosaur fossils.

The Longaberger Company, which makes baskets, made a building in Newark that perfectly matches its brand. The building was closed in 2016, and it has largely sat idle since.

Plans for the property have included a hotel, a coworking space, and, most recently, a mixed-use development, but it still has an unclear path for the future.

The First Americans Museum's 175,000-square-foot building in Oklahoma pays homage to the state's indigenous populations and their history. The design is inspired by the importance placed on the rising and setting sun by Native populations, with the Remembrance Walls being aligned with the sunrise.

The central half-dome is supported by 10 pillars of various stones, each representing a 10-mile stretch traveled by Native people during forced removal from their original homelands, according to the museum's website.

In 2009, Travel + Leisure famously called The Portland Building "one of the most hated buildings in America," and its reputation is split among architecture critics. But its shapes, strange geometric clashes of glass and stone, make it the weird building that Portland most deserves.

Frank Lloyd Wright's 1935 masterpiece Fallingwater remains Pennsylvania's greatest work of architecture. Water falls from each level of the building into the one below, perfectly integrating with the landscape.

Built as a summer residence for Cornelius Vanderbilt II, The Breakers mansion in Newport has 70 rooms across 138,300 square feet, making it one of the largest houses in the US and an icon of Gilded Age architecture.

In South Carolina, the International African American Museum stands on top of 18 13-foot pillars that keep the museum from touching the sacred ground on which it was built.

The museum is situated on the historic site of Gadsden's Wharf in Charleston's Cooper River, which was the last and most significant disembarkation point in North America for enslaved Africans during the transatlantic slave trade, per the US Civil Rights Trail website.

The walls of the Corn Palace in Mitchell are adorned with complex murals and art that's all been made out of, you guessed it, corn. The design changes every year.

Built in 1897 for the Tennessee Centennial Exposition — and then reconstructed between 1921 and 1930 — the Parthenon in Centennial Park is a full-sized replica of the Parthenon in Athens, Greece. Today, it's open to the public as an art museum.

Designed by renowned artist James Turrell, the "Twilight Epiphany" Skyspace in Houston is a performance space that makes you feel as though you've entered another dimension.

The Natural History Museum of Utah in Salt Lake City looks like it could have been carved out of the landscape. It was designed by Todd Schliemann of Ennead Architects.

The Old Round Church in Richmond is technically a 16-sided polygon, but it's still enough of a circle to lend credence to a rumor that it was built in that shape so that the Devil had no corners to hide in.

If they're done wrong, airports can be the most insufferable place to spend a few hours. But we have to admire Virginia's Dulles International Airport, which almost looks like a futuristic aircraft itself.

Forget the idea of a dusty old home for books nobody reads. The Seattle Central Library is a miracle of modern architecture.

Construction on the Capitol started in 1793.

The United States Capitol is such a mainstay of nightly news and political pop culture that it's easy to take for granted. It's nice to step back once in a while and take in the grandeur and historical significance of this government building that reflects on America's complicated past.

Construction on the Capitol began in September 1793, and much of the structure was built by enslaved workers working alongside free Black and white laborers, per the White House Historical Association. In 2012, a marker was added to the Capitol Visitor Center commemorating the unpaid labor of enslaved people who built the nation's Capitol.

The Palace of Gold is a majestic memorial shrine located in the Hare Krishna community of New Vrindaban.

The most striking feature of the Milwaukee Art Museum is the Burke Brise Soleil, a towering sunscreen with a 217-foot wingspan. It folds and unfolds twice a day.

This wacky-looking building is in the middle of the remote Wapiti Valley. In 1971, architect Francis Lee Smith started building the structure by hand as his and his family's home. After completing the first floor in 1973, he could not stop building. He died after falling from one of the balconies in 1992.

Alabama's capitol served as the first capital of the Confederacy, and there's a brass star on one of the porticos marking the spot where Jefferson Davis was sworn in as its president, according to the Alabama Historical Commission.

The building that stands today was constructed in 1851, after a fire burned down the original building in 1849, according to the Alabama Historical Commission.

One of the more famous parts of the capitol grounds is the Avenue of Flags. It has the flag of every state, plus a native rock from each state at the base of its flag. It was dedicated in 1968, according to Exploring Montgomery.

The Alaska State Capitol, completed in 1931, doesn't look much different from any other office building in Juneau, save for the marble columns. According to Alaska's official website, it is one of the few state capitols that do not feature a dome.

As The New York Times reported in 1981, neither the building nor the location was popular with locals — both were chosen because of cost concerns shaping both construction and relocations. Voters approved a measure in the 1970s to move the capitol, but the effort ultimately failed.

As recently as 2022, Alaskan senators sponsored a bill to move the capital, this time to Willow, reported Alaska Public Media, but for now, Juneau remains the Last Frontier's capital city.

Arizona's capitol was dedicated in 1901. It stopped being the home of the legislative branches of government in 1960, and by 1978, all government officials had been moved to other buildings nearby in an area called the Capitol Complex.

The original building was then officially converted into a museum open to the public.

Arkansas' capitol took 16 years to complete. Construction lasted from 1899 to 1915, and the building was originally designed by architect George R. Mann, with later revisions by Cass Gilbert, according to the Encyclopedia of Arkansas.

This building replaced the State House, which is now the Old State House Museum, according to Arkansas Heritage.

The building was constructed between 1860 and 1874, and designed by Reuben S. Clark. It has been listed as a California Historical Landmark since 1974, according to the Historic State Capitol Commission.

Its design was based on the US Capitol in Washington, DC, among other well-known American buildings, according to the State of California Capitol Museum.

The California State Capitol is located inside the 40-acre Capitol Park, which contains trees from around the world, a World Peace Rose Garden, and the Civil War Memorial Grove.

The Colorado Capitol, which was completed in 1901, was also designed to look like the US Capitol, but with a Colorado twist: The dome is covered in real gold leaf donated by gold miners to reference the Colorado Gold Rush from 1858 to 1861, according to the Colorado General Assembly.

The current Connecticut State Capitol is actually the third capitol the state has had since the American Revolution. This one, designed by Richard M. Upjohn, opened in 1879, according to Connecticut's official state website.

The golden dome is surrounded by six pairs of statues representing agriculture, commerce, education and law, force and war, science and justice, and music, according to the State Capitol Preservation & Restoration Commission.

The Delaware Legislative Hall was dedicated in 1933 and replaced the Old State House, which is opposite the Hall on the capitol mall. It was designed in the Colonial Revival style by E. William Martin, according to Delaware's official state website.

The United States Capitol is located on Capitol Hill in DC. It was in construction for decades, partially destroyed in 1814, and then finally finished in 1829, according to Architect of the Capitol. The famous, gigantic dome was later added during an expansive addition in 1855, designed by Thomas U. Walter.

Atop the dome sits the "Statue of Freedom," a 19-foot statue of a woman wearing a battle helmet, holding a sheathed sword in one hand, and a laurel wreath and shield in the other. She's been there since 1863, according to Architect of the Capitol.

The current capitol, also called the New Capitol, is located directly in front of the original — together, they form the Capitol Complex. The New Capitol was built in 1977 by architect Edward Durell Stone and the firm of Reynolds, Smith, and Hills, according to the Florida Capitol website.

The website reports the building was designed in an "international style to reflect a modern Florida," and includes a 22-story central tower.

The Old Capitol still stands, and it was restored to its original 1902 glory in the '80s. Currently, the building is the Florida Historic Capitol Museum.

Georgia's capitol was finished in 1889 and designed by Willoughby J. Edbrooke and Franklin P. Burnham, according to the city of Atlanta's website. It sits on the site of the former Atlanta City Hall/Fulton County Courthouse, which was there from 1854 to 1994.

According to the city, it's one of 43 National Historic Landmarks in the state.

At the dedication of the Hawaiian capitol in 1969, then-Governor John A. Burns explained the design of the building, the Honolulu Star Advertiser reported.

"In this great State Capitol there are no doors at the grand entrances which open toward the mountains and toward the sea," he said. "There is no roof or dome to separate its vast inner court from the heavens and from the same eternal stars which guided the first voyagers to the primeval beauty of these shores."

The building is also surrounded by a reflecting pool meant to symbolize the Pacific Ocean, which surrounds the chain of 137 recognized islands that make up Hawaii, according to the State of Hawaii.

Idaho's capitol was designed by architects J.E. Tourtellotte and Charles Hummel, and was constructed between 1905 and 1920. According to Idaho's Capitol Commission, it's the only capitol in the US that is heated by geothermal water. It comes from a spring 3,000 feet underground.

According to a pamphlet by the Illinois Secretary of State's office, the current capitol (the state's sixth) was completed in 1888, 20 years after crews broke ground. At the time of its construction, the limestone dome was illuminated by 144 gas jets. However, the carbon emitted by those jets eventually turned the dome black.

It took 100 years, but it was finally cleaned in 1986.

According to the Indiana Department of Administration, Indiana's capitol was completed in 1888, and is home to all executive offices, the Indiana State Senate, the Indiana House of Representatives, and the Indiana State Supreme Court, among others. It was constructed with Indiana limestone.

The large golden dome is 23 carats, and the entire building is 275 feet tall, according to a visitor's guide. It's been re-gilded four times since its construction in 1886.

Overall, Iowa's capitol has a total of five domes, making it the only capitol in the US with five.

Kansas' capitol dome is topped with a statue called "Ad astra" (Latin for "to the stars"), which is part of the state's motto, "ad astra per aspera" ("to the stars through difficulties"), according to the Kansas Historical Society.

The statue itself is a bronze depiction of a warrior from the Kansa tribe (also known as the Kaw Nation or Kanza), who call Kansas home and gave the state its name.

The entire building took 37 years to construct, also according to the Kansas Historical Society, from 1866 to 1903. 

Kentucky's capitol was designed by Frank Mills Andrews, according to Kentucky's official state website. There are also statues lining the front portico that represent Kentucky, the central figure, with Progress, History, Plenty, Law, Art, and Labor as her "attendants," according to the state website.

The current building is the fourth capitol in the state, and it was completed in 1910.

The Louisiana Capitol is just one of nine capitols in the US that doesn't feature a dome — and at 450 feet tall (or 34 floors), it's also the tallest capitol in the country, according to Louisiana's House of Representatives.

It was dedicated in 1932, without the person who had spearheaded the effort to build it, Senator Huey P. Long, a controversial figure in Louisiana's history, as reported by Encyclopedia Britannica.

The capital of Maine was originally Portland when the state broke away from Massachusetts in 1820. But when Mainers asked for a more centrally located capital city, Augusta was chosen in 1827, according to the Maine State Legislature. The building was completed by 1832.

The State House's dome is topped with a female figure of Wisdom, which was designed by sculptor W. Clark Noble of Gardiner, a town 6 miles from Augusta.

Maryland's State House is the oldest capitol in continuous legislative use in the US, built in 1779, according to its official website. It's also the only state capitol to have once served as the US capitol when the Continental Congress met there from 1783 to 1784, according to the website.

The Massachusetts State House, built in 1789, originally had a wooden dome, but Paul Revere's own company was responsible for covering it in copper in 1802, CBS News reported.

And the land it was built on? It used to be owned by none other than John Hancock, who was Massachusetts' first elected governor.

The floors of Michigan's capitol, which was dedicated in 1879, are made of limestone and have visible fossils in them, as you can see on the capitol's official website.

According to Explore Minnesota, the state's capitol is the second-largest self-supporting marble dome in the world, only behind St. Peter's Basilica in Rome.

Architect Cass Gilbert insisted on using Georgia marble for the dome, according to the Minnesota Historical Society. Some were critical of using out-of-state materials, so as a compromise, the contractor leased the quarry in Georgia and imported the rough marble so Minnesotans could do the work in-state.

It took nine years, but was completed in 1905.

Designed by architect Theodore Link and constructed between 1901 and 1903, Mississippi's state capitol was built on the site of an old state penitentiary, according to the state capitol's official website. The building spans 171,000 square feet and features 4,750 original electric light fixtures, as well as an 8-foot statue of an eagle on the top of its dome.

Missouri's state capitol was completed in 1917, according to its official website. Ceres, the goddess of grain, sits at the top of its dome.

In addition to Missouri's state legislature, the 500,000-square-foot building houses the Missouri State Museum with exhibits about the state's history and natural resources.

The main building of Montana's state capitol was completed in 1902, and its two wings were added in 1911 and 1912, according to the Montana Historical Society. Inside, the building features works of art such as the mural "Lewis and Clark Meeting Indians at Ross' Hole," painted by Charles M. Russell in 1912.

Nebraska's state capitol was designed by architect Bertram Grosvenor Goodhue and completed in 1932, according to its official website. The 400-foot tower is topped with a 19-foot bronze statue called "The Sower."

It is the only state legislature to be unicameral, meaning it only has one chamber.

Nevada's state capitol was built from 1870 to 1871 out of sandstone sourced from a quarry belonging to Abe Curry, the founder of Carson City, according to Travel Nevada. It features a silver-colored dome, a nod to Nevada's nickname as "the silver state."

The New Hampshire State House was constructed between 1816 and 1819 with locally sourced granite from Rattlesnake Hill in Concord, according to the New Hampshire Division of Historical Resources.

In 1818, a wooden sculpture of an eagle painted with gold was installed on top of the capitol dome. It was replaced with a copper replica in 1957, but the original sculpture can be viewed on display inside the capitol, according to EverGreene, the architecture firm that restored the State House's gold-plated dome.

After Maryland, New Jersey State House is the second-oldest capitol still in use, completed in 1792, according to the state of New Jersey's official website. Much of the original building, designed by architect Jonathan Doane, was destroyed in a fire in 1885.

Architect Lewis Broome restored the capitol and added a cast-iron dome plated with copper and gold and featuring the Latin phrase "Fiat Justitia Ruat Coelum," meaning  "There must be justice even though the heavens fall."

New Mexico's capitol, known as the Roundhouse, is the only round capitol in the US, according to Santa Fe's official tourist website. Architect Willard C. Kruger modeled the design after the Zia sun symbol, which he also incorporated into the capitol rotunda skylight. The symbol is also part of New Mexico's state flag.

When New York's state capitol in Albany was finally finished after 32 years in 1899, it was at a cost of $25 million, making it one of the most expensive government projects in the US. In 2013, The New York Times reported the figure was equivalent to more than half a billion dollars today.

Inside the granite building, visitors can find 25 murals by William deLeftwich Dodge in the Governor's Reception Room.

Completed in 1840, North Carolina's 3-story capitol includes a copper dome, according to the National Park Service.

North Dakota's state capitol is the tallest building in the state at 241 feet and 8 inches tall, according to the official government website. The Art-Deco structure is nicknamed the "Skyscraper on the Prairie," according to the Society of Architecture Historians.

Construction of the Ohio Statehouse took over 20 years, from 1839 to 1861, according to its official website. Much of the work was done by prisoners at Ohio Penitentiary, some of whom left graffiti on the walls that was uncovered during restoration work, the website says. Built in the Greek-Revival architecture style out of Columbus limestone, the Statehouse is a designated National Historic Landmark.

Built in 1917, the dome on Oklahoma's capitol was added more recently, in 2002, according to the Oklahoma Historical Society — it was left out of the original construction due to costs. The grounds of Oklahoma's capitol also had active oil rigs until 1986. The building was added to the National Register of Historic Places in 1976.

Oregon's Art Deco capitol is made of white Vermont marble with a gold statue of an "Oregon Pioneer" atop the dome, according to the capitol's official website. In-person guided tours are paused due to construction.

Pennsylvania's capitol, designed by architect Joseph Huston, cost $13 million to build when it was completed in 1906, which would be over $403 million today, according to the Bureau of Labor Statistics.

The building's 272-foot dome is decorated with green glazed terra cotta tile, according to the capitol's official website.

The Rhode Island State House, built between 1895 and 1904, features the fourth-largest freestanding marble dome in the world, according to the Rhode Island Restoration Committee's official website. It has been listed on the National Register of Historic Places since 1970.

The construction of the South Carolina State House began in 1854, but halted due to the Civil War. The building still features cannonball marks from when the Union army captured Columbia in 1865, according to Discover South Carolina. The State House was finally completed in 1903, and it was designated as a National Historic Landmark in 1976, according to the South Carolina Department of Archives and History.

A portrait of state senator Clementa Pinckney, who was killed in the 2015 shooting at Charleston's Mother Emanuel AME Church, hangs in the Senate Gallery.

South Dakota's state capitol was constructed between 1905 and 1910, not long after South Dakota became a US state in 1889, according to the South Dakota Bureau of Administration. An annex was added in 1932. The Neoclassical building features scagliola plaster columns, war memorials, and stained-glass windows, according to Travel South Dakota.

The Tennessee State Capitol opened in 1859. The architect, William Strickland, died during its construction in 1854 and was buried on the capitol grounds along with President James K. Polk and first lady Sarah Childress Polk, according to the Tennessee State Museum.

Completed in 1888, the Texas State Capitol dome is topped with a statue of Libertas, the goddess of liberty, according to the official website for the Texas House of Representatives. It stands 14 feet taller than the US Capitol.

Utah's State Capitol was designed by architect Richard K.A. Kletting and was completed in 1916, according to its official website. The rotunda features bronze and marble statues of Native American leaders, LDS pioneers, and US presidents such as Abraham Lincoln, according to its website.

The Vermont State House, designed in the Greek Revival architecture style, dates back to 1857, according to the National Park Service. A statue of Ceres, the goddess of agriculture, adorns the top of the dome.

Thomas Jefferson designed Virginia's state capitol to look like the ancient Roman temple of Maison Carée, according to the Virginia General Assembly's official website. The building also features a bronze statue of Jefferson, who is depicted holding the capitol's architectural blueprints.

The Washington State Legislative Building features the tallest freestanding masonry dome in North America at 287 feet, according to the Washington State Department of Enterprise Services. Designed by Walter Wilder and Harry White, it was completed in 1928.

West Virginia's capitol, designed by Cass Gilbert, took eight years and almost $10 million to construct before its completion in 1932, according to its official website. The dome stands at 293 feet tall — 5 feet higher than the US Capitol in Washington, DC.

Wisconsin's state capitol features the only granite dome in the US, according to Travel Wisconsin. On top of the dome, a gilded bronze statue by Daniel Chester French is aptly named "Wisconsin."

Wyoming's state capitol, constructed between 1886 and 1890, was built in the Renaissance Revival architecture style, according to the Wyoming Department of Administration and Information. It is one of 20 state capitols designated as a National Historic Landmark, according to the National Park Service.

After the attack on Pearl Harbor in 1941, a temporary bomb shelter was built in the Treasury Department in 1941.

When Roosevelt expanded the East Wing and added a second story in 1942, a new presidential bomb shelter was built beneath it. It featured a bedroom and bathroom, as well as ventilation masks, food, and communications equipment, all fortified behind concrete walls.

"The best time to construct something underground is when you're building something above ground, especially when it comes to the White House," Costello said.

During these White House renovations, Roosevelt also converted a cloakroom in the East Wing into a movie theater.

The four-year, $5.7 million renovation was required to reinforce the entire White House structure, which had begun to sag into the ground. The Trumans temporarily moved to Blair House as workers hollowed out the White House.

"When they do the Truman renovation, where they essentially gut the inside of the house and then rebuild it from the inside out with concrete and steel, they really are fortifying the White House to serve as a bomb shelter," Costello said.

As the world entered the age of nuclear weapons, the PEOC was also expanded and updated during this renovation.

"As there are these wider changes around the world, they impact how presidential security is revisited, reassessed, and then adapted as needed," Costello said.

When the first plane hit, Cheney turned on the news in his office at the White House. After the second plane hit, his lead Secret Service agent burst in to escort him to the PEOC, Cheney said in an interview with the American Enterprise Institute in 2011.

Cheney said the Secret Service agent "put one hand on the back of my belt, one hand on my shoulder," and "literally propelled me out of my office."

Cheney was joined in the PEOC by staff members, including National Security Advisor Condoleezza Rice, Transportation Secretary Norman Mineta, and Presidential Counselor Karen Hughes. He advised President George W. Bush, who was in Florida at the time, not to return to Washington, DC, marking the first time in US history that the continuity of government operations plan was implemented.

Rare photos of the PEOC on September 11 were released by the National Archives in 2014 as part of a Freedom of Information Act request, offering a glimpse inside the top-secret space.

"As far as I'm aware of, I think those are the only publicly released ones, and they were publicly released because they were forced to be released," Costello said of the images.

The photos showed a conference room with phones, video call capabilities, television screens playing news reports, world clocks, and a map of the United States.

"I was hustled inside and downstairs through a pair of big steel doors that closed behind me with a loud hiss, forming an airtight seal," she wrote in "Spoken from the Heart" of her experience on September 11.

"I was now in one of the unfinished subterranean hallways underneath the White House, heading for the PEOC, the Presidential Emergency Operations Center, built for President Franklin Roosevelt during World War II. We walked along old tile floors with pipes hanging from the ceiling and all kinds of mechanical equipment."

Laura Bush wrote in her memoir that George W. Bush arrived at the PEOC at 7:10 p.m. on September 11.

When the Secret Service suggested that she and her husband spend the night in the secure bunker, Laura Bush wrote that they declined because the foldout bed "looked like it had been installed when FDR was president."

It was widely reported that Trump was taken to the PEOC as a precaution when protesters breached temporary fences outside the White House. Trump told Fox News Radio that he had visited the bunker to inspect it, not to take shelter there.

"I was there for a tiny, short little period of time," Trump said. "They said it would be a good time to go down and take a look because maybe sometime you're going to need it."

The White House announced that the new ballroom would measure 90,000 square feet, seat around 1,000 people, and serve as a "much-needed and exquisite addition." Trump and other "patriot donors" will fund the $400 million project, the White House said.

The National Trust for Historic Preservation's lawsuit alleged that Trump had no legal authority to demolish the East Wing and replace it with a ballroom.

In March, a federal judge's ruling halted above-ground construction until Congress approves the project, but allowed work related to "the safety and security of the White House" to continue.

Trump then confirmed what the lawsuit had alluded to: a new and improved PEOC was in the works.

"The military is building a big complex under the ballroom, which has come out recently because of a stupid lawsuit that was filed," he told reporters on board Air Force One on March 29.

He added that the ballroom would essentially function as a "shed" for the secure facility below.

"We have bio defense all over," he told reporters on March 31. "We have secure telecommunications and communications all over. We have bomb shelters that we're building. We have a hospital and very major medical facilities that we're building. We have all of these things, so that's called: I'm allowed to continue building as necessary."

A federal appeals court allowed construction to continue temporarily while it reviews the case more closely, with a formal hearing scheduled for June 5.