A ruined mansion hidden in the woods of the Hudson Valley, home of a tragically doomed romance.

The summit Roosevelt conquered before he descended to become The Chief.

This former theme park in New York's Adirondack Mountains fell into ruin before being resurrected as a state-run campground

An old abandoned mining town in The Adirondacks where Theodore Roosevelt first learned of the shooting of President William McKinley.

This old cement mine has been used as everything from a mushroom farm to a recording studio.

An abandoned 19th century quarry in the middle of the woods, remade by unnamed wanderers into a massive series of rock thrones.

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

Hanging over one of Japan's "hidden valleys," these vine bridges must be remade every three years.

Known for the tunnel that leads visitors to the water.

A Hawaiian stairway to heaven—that you can't climb.

A tunnel of hardened lava along Maui’s famous Road to Hana.

A gargantuan crystal kingdom.

Bowl in splendor, if you're lucky.

A hyper-luxurious, 12,000- square foot home might be buried beneath Queens, still waiting to protect you from nuclear missiles.

This famous bridge twisted itself into oblivion, but not for the reason you might think.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

This impressive tunnel was dug entirely by hand over the course of 36 years.

This dramatic sea spire is home to the world's rarest insect and is part of the lost continent of Zealandia.

One of the deepest blue holes in the world.

A spectacular cave and a beguiling lake.

Stalactites and stalagmites in a beautifully lit cave.

In the middle of downtown Brooklyn lies a 165 year old secret hidden right below the surface (closed to the public indefinitely).