An ethereal glowing blue ocean cave in Croatia.

Holy Hindu shrine in an enormous, monkey-filled limestone cavern.

Snow-capped peaks, colorful waterfalls and stunning vistas on the edge of the Himalayas.

Rock-cut caves and 7,000 Buddhist sculptures carved into the nearly sheer face of a sandstone mountain.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

A former imperial sea-fortress and Soviet prison.

Museum preserving torture methods from the past.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

On Japan's Tashirojima Island, cats are king.

This attraction was abandoned after the Chernobyl disaster.

An Italian hillside ghost town.

This French ghost town from World War II has been left as a memorial to German atrocities during World War II.

Once the most densely populated place in the world, this island is now a ghost town.

A battle between nature and architecture in the Cambodian jungle.

Every equinox this Maya pyramid puts on a spooky ancient light show.

This notorious Canadian mental institution was home to some of the first LSD experiments and origin of the word "psychedelic."

Abandoned city hidden from the world by tropical forest and isolation on the coast of Kenya.

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

A sunken idol welcomes parishioners to Davy Jones' Locker.

A formerly abandoned mental institute, now back in business.

Venice's "Island of the Mad."

This hospital once pioneered the use of electroencephalograms, but fell into maltreatment, abuse, and eventual abandonment.

A lovers' beach, tucked below the surface of the island, provides a safe haven for romance.

An underwater city for the dead.