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

A long abandoned hospital building on the outskirts of NYC.

Elevated freight railway turned wildly successful urban park.

World's first "penitentiary," meant to be humane, drove men insane.

Rusting, graffiti-covered tanks litter the beach of this island, once used by the U.S. military for target practice.

A former poultry store that looks like a giant duck and is one of the "seven wonders" of Long Island.

This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

A small peaceful park and waterfall tucked amid the urban grind of Midtown Manhattan.

This former crime corner has been turned into an eclectic community center.

Twice a day one of these tragic bronze mariners drowns with the tide to remember all those the sea has taken.

The site of a tragic massacre that spawned a multimedia franchise.

The end of the 4 Line is also the end of the line for 300,000 souls in one of NYC's most illustrious cemeteries.

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

This once luxurious Catskills resort is now a haunting ruin.

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

This abandoned seaside fortress is now simply an imposing ruin being taken back by nature.

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

A crumbling stone stable and carriage house are all that remain of a manse that was once filled with Egyptian artifacts.

To avoid the demolition costs this abandoned drawbridge was simply left in the up position.

This fairy tale-themed amusement park is now abandoned, and childhood metaphors abound.

Abandoned Coast Artillery fort now serves as graffiti canvas and sightseeing vantage point.

Once in a state of dilapidation, this candy-inspired fortress is now being revived.

A formerly abandoned mental institute, now back in business.

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