New York City's smallest piece of private property.

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

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

Architecturally stunning library serves as the hub of Finnish scholarly life and culture.

An extraordinary library and archive dedicated to the history of the Arctic and Antarctic poles.

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

This Queens beer hall preserves a German culture and language that is all but lost.

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

A small museum filled with over 1,000 clocks, and one particular clock calibrated to run until the year 9999.

The notorious headquarters of a corrupt political machine.

Tucked away amidst some of the most famous addresses in the world is New York's only fraction of a street.

A grand New York post office that is home to mailman Santas, scraps of postal history, and a pneumatic mail system.

Cryptic messages embedded in the New York City sidewalk.

The New York hotel where tragic visionary Nikola Tesla spent his final hours, destitute and alone but for the pigeons.

Built as a gift to the hottest tastemaker of the time, these hidden quarters remain an Art Deco showpiece.

Cheap pizza and all of your naughty bedroom needs housed in a stunning example of Art Nouveau architecture.

This unmarked and unloved Manhattan subway grate created one of the most iconic images in American cinema.

This semi-hidden Manhattan restaurant is based out of a loading dock.

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

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

Hidden in an ordinary Midtown building is a one-room museum dedicated to the greatest escape artist.

This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

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

The last remnants of what was once one of the world's grandest hotels can now be found in a Manhattan subway station.