9 Notable Buildings With Secret Floors

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iStock

Secret floors have long captured the imagination; conspiracy theorists love to imagine that government buildings keep their darkest secrets within sealed-off stories. In the 1960 Twilight Zone episode “The After Hours,” the ninth floor of a department store is where the mannequins mysteriously come to life. Meanwhile, the hidden 7th-and-a-half floor of the Mertin-Flemmer building in New York was a portal for John Cusack into the actual brain of John Malkovich in the movie Being John Malkovich.

While these mysteries may have come from a writer’s imagination, there are notable buildings that have whole secret floors right under your nose—if you know where to look.

1. THE EMPIRE STATE BUILDING, NEW YORK

One of the world’s most iconic and recognizable skyscrapers, the Empire State Building is also one of Manhattan’s premiere tourist destinations. The gleaming Art Deco elevators speed thousands of visitors to the observation deck on the 86th floor every day, and there’s also an observation pod on the 102nd floor. But just above, hidden out of sight, is the secret 103rd floor. Off-limits to the public, there is no glass protecting visitors from the elements, just a narrow walkway surrounding the top of the building. Original plans are thought to have allowed airships to dock to the top of the Empire State Building, with passengers disembarking on the 103rd floor, and the 102nd being their official port of entry into the United States. The plan never came to fruition, however, and the hidden 103rd floor remains sealed off high above New York City.

2. THE FIFTH FLOOR OF THE YANGGAKDO HOTEL, PYONGYANG, NORTH KOREA

For Calvin Sun, of the adventurous travel blog Monsoon Diaries, a hotel in the world’s most isolated nation held a particularly odd secret. The hotel Yanggakdo’s elevator has no 5th floor. Getting out of the elevator on the 6th and walking down, his group reached something peculiar: an entire concreted hidden floor, filled with locked doors and no people. The floor was covered with what looked to be government-issued propaganda posters, with messages like “Let’s prepare thoroughly in order to defeat the invaders” and “Our General is the best.” Other intrepid adventurers have reported bunkers, steel doors, official-looking men with computers, and others listening to headphones. Some have speculated that there is another floor hidden within the 5th, but its purpose remains unknown.

3. THE GREENBRIER RESORT, WEST VIRGINIA

The Greenbrier is a luxury hotel and resort located amid the mountains of West Virginia. The local waters have been attracting guests since 1778, and the glittering guest list of the hotel, now a National Historic Landmark, has included 26 presidents. But hidden under the glamorous rooms and sprawling grounds is a massive underground complex, codenamed Project Greek Island. During the Cold War, it was built to hold the entire United States Congress in safety—just in case Washington was attacked by a Soviet nuclear strike.

The 112,000-square-foot bunker was big enough to hold both the House of Representatives and the Senate, and came complete with six months’ worth of food, 25-ton blast doors, decontamination chambers, water purification equipment, and its own hospital. The government’s construction of Project Greek Island was covered up by the building of a new west wing added to the existing hotel. To avoid detection, the huge amounts of land unearthed in the creation of the project were used in a new golf course, while the army of workers posed as employees of a fake audiovisual company called the Forsythe Associates, who “maintained” the hotel's 1000 television sets.

Project Greek Island fortunately remained unused, and was never officially acknowledged until a story in the Washington Post in 1992 exposed the secret. Today tours of this remarkable relic of the Cold War are given at the hotel, which still operates as a luxury resort.

4. OUR LORD IN THE ATTIC, AMSTERDAM

Luke Spencer

There’s an old house in Amsterdam that looks much like the other Queen Anne-style homes along the canals that give this old part of the city its distinctive character. This particular house, however, holds a remarkable secret hidden away in the attic: a miniature, fully functioning church. Complete with marble altar, pews enough for 150 worshippers, and elaborate gilt decoration, the church was hidden due to the persecution of Dutch Catholics in the 17th century. Access to the clandestine church is gained by a false wall in the living room that leads to a narrow spiral staircase. Today the church is a museum, but still regularly holds services hidden away in the attic, as they have done for nearly 400 years.

5. THE NEW YORKER HOTEL, MANHATTAN

Luke Spencer

When the New Yorker Hotel opened on 8th Avenue and 34th Street in 1930, it was one of the most technologically advanced hotels in the world. It came complete with its own in-house radio station, printing press, 50-chair barber salon, and a dining room that featured a retractable ice rink and skating show to entertain the guests. With 2500 rooms, it was promoted as a “vertical village.”

Underneath the lobby was a giant power plant, occupying a hidden floor around 80 feet below the sidewalk. The DC generating plant was so huge, it was powerful enough to provide electricity for a city of around 35,000 people. The plant was also so sophisticated that one of the hotel’s most famous long-term residents, the inventor Nikola Tesla, who lived there for the last decade of his life, is reported to have wandered down under the lobby to tinker with the plant and talk with the engineers. Remarkably, the plant is still down there, the switches for the old skating rink, coffee shop lights, and ballroom silent and unused. (Much of the plant was modernized in the 1960s, however, and switched over to the alternating current Tesla championed.)

6. WALT DISNEY WORLD, FLORIDA 

Observant visitors to the Magic Kingdom, upon disembarking from the monorail and heading toward Main Street, USA, may notice that they are walking on a slight incline. Indeed Cinderella’s Castle, which lies ahead, appears to be on a hill. In reality, the thousands of daily guests are unknowingly climbing over a vast hidden complex of secret floors, rooms, walkways, and tunnels. Disney World itself is built on top of an intricate hidden infrastructure that Cast Members consider the first floor. (The entire Magic Kingdom itself is technically the second and third floor.)

The story goes that Walt Disney was walking through the original Disneyland in California, and saw a Cast Member dressed as a cowboy walking from Frontierland through to Tomorrowland. Thinking that this would ruin the fantasy illusion for the visiting children, Disney World was designed on top of a hidden 9-acre system that would house walkways for Cast Members, trash collectors, kitchens, and break rooms. Today, tours are available for adults to see behind the curtain of the Magic Kingdom.

7. JOHN HANCOCK CENTER’S 44TH FLOOR, CHICAGO

The John Hancock Center on North Michigan Avenue is one of Chicago’s most iconic landmarks. When it was completed in 1969, it was one of the tallest buildings in the world, second only to the Empire State Building in New York. But what many people don’t realize is that it is actually possible to live inside one of America’s most famous skyscrapers. The residential floors run from the 45th to the 92nd floor, but it is the 44th floor that holds all the secrets. Off-limits to all but the residents, the 44th floor is home to a vast 5200-square-foot supermarket. There is also a library, concierge service, a high-ceilinged sky lounge, and the highest swimming pool in the United States. During elections it even has its own polling station.

8. PLYMOUTH CHURCH OF THE PILGRIMS, BROOKLYN

Luke Spencer

Plymouth Church in Brooklyn Heights is a church steeped in history. One of the oldest Congregationalist Churches in New York, it was once presided over by the inspirational orator, minister, and abolitionist Henry Ward Beecher. Described then as “the most famous man in America,” his fiery anti-slavery rhetoric was so renowned that Plymouth was the only church in New York visited by Abraham Lincoln. Beecher would hold mock slave auctions on the site, where parishioners would raise money to free slaves.

But the extraordinary events on the church floor covered a remarkable secret below it: a hidden floor, with the entrance through a door behind the organ. Dry, dusty chambers, brick archways, and tunnels are all that remain of one of the principal stops on the Underground Railroad. This hidden floor provided a sanctuary for so many escaping slaves that it became known in hushed voices as the Grand Central Depot. At great risk to themselves, the brave parishioners of Plymouth Church, led by Beecher, vowed to help as many slaves as possible. “I will both shelter them,” Beecher said, “conceal them or speed their flight.” The church is still vibrantly active today, and tours are available to visit what was once one of the most secret places in America.

Luke Spencer

9. THE OLD OPERATING THEATRE AND HERB GARRET, LONDON

Luke Spencer

Hidden in the roof of St. Thomas’ Church in London is something as chilling as it is fascinating. Climbing the circular staircase of the old church to the garret (or attic) leads to one of the oldest known operating theaters still in existence. Once part of the ancient St. Thomas’ Hospital, visitors today can crowd into the tiny theater and stand on steep wooden terraces overlooking the operating table. Here 19th-century medical students would watch the pre-eminent surgeons of the day practice their craft; one notable surgeon was said to be able to amputate and cauterize a limb in under a minute.

In the attic above the theater is the old herb apothecary and garden where herbs were stored and cured. Still well-stocked today, the Herb Garret resembles a Victorian cabinet of peculiar curiosities, featuring wormwood, poppies for opium, and a “bath of sheep heads for Woman suffering from unknown illness.” After St. Thomas relocated, the church garret was sealed up and forgotten for decades, until it was rediscovered in the 1960s. Today operating as a museum, tours are available for those who want to experience the lancets, blades, and bone saws of over a hundred years ago. 

Luke Spencer

Mapping Technology Reveals 'Lost Cities' on National Geographic

Lin uses his iPad to visualize scanning data of a crusaders' fortress at the lagoon in Acre, Israel.
Lin uses his iPad to visualize scanning data of a crusaders' fortress at the lagoon in Acre, Israel.
Blakeway Productions/National Geographic

Imagine what Pompeii looked like before the lava hit, or Mayan pyramids before the jungle took over. In the past decade, scientists have been able to explore human settlements long since abandoned by using a new wave of accessible technology. Instead of needing an expensive plane and crew to fly aerial sensors, for example, explorers can mount them on cheaper drones and pilot them into previously unreachable areas. The resulting data can tell us more about the past, and the future, than ever before.

That’s the premise of Lost Cities with Albert Lin, a new TV series premiering on National Geographic on Sunday, October 20.

Lin, an engineer and National Geographic Explorer, uses cutting-edge tools to shed light on centuries-old cities in the most beautiful places on Earth. Ground-penetrating radar reveals buried structures without disturbing the landscape. A drone-mounted remote sensing method called LIDAR—short for "Light Detection and Ranging"—shoots lasers at objects to generate data, which Lin visualizes with 3D mapping software. The results suggest what the ruins probably looked like when they were new.

Albert Lin and crew in Peru
Thomas Hardy, Adan Choqque Arce, Joseph Steel, Duncan Lees, Albert Lin, and Alonso Arroyo launch the LIDAR drone at Wat'a in Peru.
National Geographic

“It’s like a window into a world that we’ve never had before,” Lin tells Mental Floss. “It’s shooting millions of laser pulses per second through a distance of air. By digitally removing the top layer of everything above the ground—trees, brush, cacti—you’re washing away the past. All of the sudden you’re left with these fingerprints—experiments in how we organized ourselves through time.”

For the six-episode series, Lin and the expert storytelling team were dispatched to the South Pacific, the Middle East, the Andes, the Arctic, and other destinations. Lin explains that while most of the sites are known to archaeologists, they’ve never been so precisely mapped in three-dimensional detail.

In the first episode, Lin travels to Nan Madol, an enigmatic complex of temples and other structures on the Micronesian island of Pohnpei. With the help of local researchers and indigenous leaders, Lin and the team scan the ruins and digitally erase trees, water, and forest undergrowth to unveil the complex's former grandeur.

“Technology and innovation have always been that gateway to go beyond the threshold, and see what’s around the corner,” Lin says. “Seeing these worlds for the first time since they were left, it’s almost like reversing the burning of the library of Alexandria. We can take the synthesis of knowledge of all these watershed moments of our human journey, and imagine a better future.”

Lost Cities With Albert Lin premieres Sunday, October 20 at 10/9c and resumes on Monday, October 21 at 10/9c on National Geographic.

What's the Difference Between Cement and Concrete?

Vladimir Kokorin/iStock via Getty Images
Vladimir Kokorin/iStock via Getty Images

Picture yourself walking down a city block. The sidewalk you follow may be obscured by shuffling feet and discarded gum, but it’s clearly made from something hard, smooth, and gray. What may be less clear is the proper name for that material: Is it concrete or cement? Is there even a real difference between the two words?

Though they’re often used interchangeably, concrete and cement describe different yet related elements of the blocks, flooring, and walls that make up many everyday structures. In simple terms, concrete is the name of the gray, gritty building material used in construction, and cement is an ingredient used in concrete.

Cement is a dry powder mixture that looks much different from the wet stuff poured out of so-called cement trucks. It’s made from minerals that have been crushed up and mixed together. Exactly what kind of minerals it’s made from varies: Limestone and clay are commonly used today, but anything from seashells to volcanic ash is suitable. After the ingredients are mixed together the first time, they’re fired in a kiln at 2642°F to form strong new compounds, then cooled, crushed, and combined again.

Cement
Cement
lior2/iStock via Getty Images

This mixture is useless on its own. Before it’s ready to be used in construction projects, the cement must be mixed with water and an aggregate, such as sand, to form a moldable paste. This substance is known as concrete. It fills whatever mold it’s poured into and quickly hardens into a solid, rock-like form, which is partly why it’s become the most widely-used building material on Earth.

So whether you’re etching your initials into a wet sidewalk slab, power-hosing your back patio, or admiring some Brutalist architecture, you’re dealing with concrete. But if you ever happen to be handling a chalky gray powder that hasn’t been mixed with water, cement is the correct label to use.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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