This truly palatial work of Communist-era architecture now sits crumbling on a Croatian beach.

This massive subterranean fissure is known as the "underground Grand Canyon."

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

A medieval fresco which reminds visitors that death will come for us all.

An intricate and amazing house built by architect Karl Junker.

According to myth, Zeus himself was hidden in this cave to escape being eaten by his dad.

The industrial monstrosity known as Bagger 258 is a colossal mining machine built in the DDR - but now left for dead in a German field.

A long spiraling walkway winds through the woods, and around a copper beech tree at the center.

A state-of-the-art medical facility from the Imperial era is now a derelict ruin.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

This abandoned Brutalist treehouse is a hidden architectural relic.

The largest collection of death masks in Ukraine.

A monument to Lenin has been transformed into a statue of everyone's favorite black-helmeted, fool-choking Sith Lord.

This derelict superstructure was a very important warning system for the Soviet military.

A subterranean Holocaust refuge within one of the world's longest cave systems.

The largest catacomb system in the world.

This attraction was abandoned after the Chernobyl disaster.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

This 15th-century island fortress later served as home to the executioners no one wanted to live near.

This remarkable cave was discovered after a shepherd watched bees enter and exit through a small fissure.

Giant marble phalluses on the sacred island of antiquity.

A minotaur, a labyrinth, and a dubious restoration pull in visitors from around the world.

Perched on a spindly rock spire in a Greek archipelago, this lighthouse would make a perfect wizard's tower.

Hidden in a secluded Greek cove is a pristine beach marred only by the rusting smuggler's hulk stranded on its shores.