Pitié-Salpêtrière was the dumping grounds for women who received the dreaded diagnosis of "hysterical."

Got apples?

Egyptian Revival movie palace abandoned for decades and restored in 2013.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

The studio of influential composer Charles Ives is perfectly reconstructed, hidden in the back of the American Academy of Arts and Letters.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

Hidden in plain sight on a pair of Manhattan subway tunnels are a pair of public instruments that sing to each other.

A room in New York City that contains 250 cubic yards of dirt worth a million dollars.

This Wall Street bar was once a hub of revolutionary activity where Washington famously bid farewell to his troops.

An accidentally hidden library containing the ephemeral history of New York.

Once the tallest building in the world and the site of "the highest dinner ever held in New York" this building now holds the most expensive penthouse in the city.

The oldest bibliophilia club in America, with exhibitions on historic books and graphic arts.

An unassuming secret door once led to a legendary watering hole.

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

One of only two commuter aerial tramways in the United States.

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

Blighted Irish field and the ruins of a 19th-century cottage on the edge of urban Manhattan.

Peek through the gates at this oasis from the city, full of Old English charm.

On the top floor of an upscale department store stands a lavish restaurant housed in a replica of a luxury French dining car.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

Everyone from Mark Twain to Teddy Roosevelt has a pipe hanging from the walls of this historic chophouse.

Hot springs monkey spa in the middle of Hell's Valley.

An exquisite tunnel of cascading flowers.

On Japan's Tashirojima Island, cats are king.