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

A forgotten relic from New York's bygone trolley system hides in plain sight under a bridge.

This small New York museum celebrates the mountainous artwork of a Russian mystic.

The world’s largest collection of Tiffany glass sits in a warehouse in Queens.

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

Though its celestial ceiling is impressive, the true star is the vast collection of French books.

Nature and beauty amidst pollution and industrial wreckage.

Guerilla gardeners reclaimed this abandoned railroad land literally putting down roots.

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

This outdoor gallery of sculptures along the East River was once a landfill.

A once crucial portion of the Long Island railroad still lays abandoned, waiting to be turned into an urban park.

Where the four original members of the Ramones hung out and revolutionized punk rock.

A uniquely lettered street sign marks the corner where the iconic word game was invented.

A menagerie of concrete animals brought together from across New York City's parks.

A New York warehouse filled with an enormous amount of goods saved from the landfills and donated for creative use.

This once-grand marvel of engineering is now 41 miles of scenic hiking trail.

This dilapidated castle-like structure overlooks the Hudson River at one of its widest points and was once home to nuns.

Nondescript elevator doors open to reveal a stunning, surreal world.

A beautiful, historic location open to the public.

America's greatest forgotten garden and the former stomping grounds of Son of Sam.

Along the Palisades skyline are the ruins of a large mansion built in 1911 and demolished in the 1930s.

Self-sufficient greenhouse floating on the Hudson River.

In 1986, Keith Haring was arrested for painting this anti-drug mural on a Harlem handball court.

From scholastic to sepulchral - now under reconstruction.