A graffiti Mecca welcoming artists from around the world.

A crumbling hospital from the 1850s on Roosevelt Island.

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

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

A New York garbage depot holds a secret collection of weird and wonderful refuse.

From scholastic to sepulchral - now under reconstruction.

Read between the lines of the subway map to find the hidden abandoned Civil War fort.

All that remains of a magnate's dream home is a historic gate and an abandoned public pool.

The loneliest island in New York.

A former connection to City Island, it has been abandoned since the 1930s.

A millionaire's abandoned swimming pool from the gilded age of one of America's most distinguished families.

Yale University's home for rare works, including the mysterious Voynich Manuscript.

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

An abandoned horticulture institute gloomily presides over rows of derelict and vine-wrought greenhouses.

A religious-themed park filled with folk art to bring biblical stories to life that fell into disrepair and now being restored.

This derelict building used to house infirm Freemasons, their widows, and orphans.

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

These World War I shooting range tunnels are now haunted halls of underground graffiti accessed through the roots of a tree.

One of the earliest bowling lanes in the U.S. doubled as a sewing school during a time when women had little job opportunity.

Connecticut's shot tower is near the end of its life.

Oldest existing church in New York and the inspiration for Washington Irving's "The Legend of Sleepy Hollow."

An Escher-inspired library dedicated to the wonders of the human mind, yet closed to the public.

The home of one of America's most wealthy industrialists is now a historic site that remembers a more decadent time in the country's history.

Collapsing castle on the Hudson river was once the storage site of military surplus business.