Decades after testing the polio vaccine on unwitting patients, this historic mental hospital sits in ruin.

This otherwise innocuous bodega was once the headquarters of the most feared assassin's guild in American history.

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

Finally, you don't have to be a pious Swedish seaman to relax like one.

Historical figures from New York City's Catholic community reside in Midtown.

This interactive gallery makes you feel like you've stepped into a fantasy world filled with whimsical monsters.

A living archive of urban activism and space reclaimed.

Named the fifth most beautiful building in America in 1885, this former courthouse boasts the best view in the Village.

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

This iconic tattoo shop has its own onsite museum with artifacts from the early history of modern body art.

Hordes of precariously balanced stone figures crowd the shores of the Hudson River.

“Invented in Key West, Perfected in Brooklyn."

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

The beautiful tunnel that ran from the lobby to Penn Station is still hidden underneath 34th Street.

A once grand hotel is being retaken by the wilderness it once capitalized on.

During the holidays, a vintage subway train whisks New Yorkers back in time.

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

Behind a bodega is a small museum of relics and ephemera showcasing the history of New York.

A band of aerialists and circus performers putting on incredible shows in East Williamsburg.

The oldest surviving synagogue in New York City is now a soaring art space.

Tucked in a nondescript downtown Brooklyn mall is a bar containing a remarkable turn of the century anatomical wax collection last seen in 1920s Berlin.

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

New York City's smallest piece of private property.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.