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

A bit of retro transportation flair preserved in the world's largest department store.

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

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

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

Pulled from the rubble of one of the worst modern tragedies, a steel crossbeam became a symbol of hope for New Yorkers.

This sculpture by artist Fritz Keonig survived the 9/11 attacks and now stands as a monument to the victims.

Home to a dizzying array of letterpress blocks with a rich history.

Unrepaired walls from a 1920 anarchist bomb attack.

This New York holdover was built to provide housing for shopgirls and still does not allow men above the lobby.

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

New York City's smallest piece of private property.

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

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

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

This lower Manhattan bar is set up in an old bank vault that rests beneath a skyscraper that hides even more historic splendor.

A Marxist summer camp full of fantastical statues lies tucked away and forgotten in the forests of Moscow.

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

A crumbling hospital from the 1850s on Roosevelt Island.

Once the fallout shelter of a dictator, this sprawling bunker is now a combined history museum and contemporary art gallery.

Hundreds of thousands of concrete bunkers crowd Albania long after the fall of Communism.

Climb into Albania's communist history while enjoying a spectacular ocean view.

The former home of a foreign correspondent who reported on Korea’s independence movement has been restored and is open to the public.

Step into a cartoon at this Seoul café that aims to evoke a two-dimensional scene.