What was once a trend-setting, phrase-coining icon of architectural splendor is now a rotting, forgotten hulk.

Naturally formed white marble arch housed in an abandoned marble quarry from the 1800s.

One New Hampshire alleyway has become home to a public gallery of feline art.

The walkable ruins of an 19th century hotel, destroyed in a horse cremation gone wrong.

The macabre graffiti spectacle in a quarry in a Massachusetts forest reservation.

Overgrown ruins of a turn of the century island fort that sees very few visitors.

The remains of a 19th century spring, and the site of an infamous unsolved murder.

A graffiti Mecca welcoming artists from around the world.

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

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.

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

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

An abandoned Gold Coast-era mansion once intended for the exiled ruler of Albania, who never arrived.

The abandoned grounds and derelict greenhouses of this once-magnificent Edwardian estate are now a nature preserve open for exploration.

A former copper mine which became a truly unsuccessful prison.

Beneath the mossy overgrowth covering this once-sprawling campus lies decades of history and the secrets that come with it.

These etchings reveal the history of a long-gone quarantine site.

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

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

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

Protecting the future of some of the rarest and most misunderstood mammals of North America.

The abandoned ruins of America's first private zoo are open for exploration in the Catskills.

A reliquary of pop culture marvels, including the world's largest (and most terrifying) Jack-in-the-Box.