An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

The haunting, dilapidated remains of a former poorhouse on Staten Island's Greenbelt.

This ruined fort hidden at the top of Central Park can't seem to keep from losing its historical plaques.

One of New York's best collections of pinball is hidden in a secret bar in the back of this laundromat.

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

A celebration of capitalism in Midtown.

A tunnel once abandoned now thrives with graffiti art as an off-limits makeshift gallery.

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

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

This beautiful building in the heart of Manhattan's Financial District was empty for decades.

A crumbling hospital from the 1850s on Roosevelt Island.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

La Monte Young and Marian Zazeela's "Dream House" will immerse you in an ever changing world of sound and light.

A town church once nearly submerged by the damming of a river is now hauntingly visible as the water recedes.

What looks like a normal building is really a hollow facade hiding a subway vent.

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

The Argonaute submarine was the French navy's pride and joy in the 1950's.

A modern-day Lascaux cave underneath Paris.

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

A wild Hollywood resort thwarted by mosquitoes.

A museum of carnival attractions where you are invited to ride the rides.

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

One of many reminders of Tesla's scientific contributions overlooks the falls which inspired him.

An eerie, derelict amusement park in Berlin.