Cave on extinct volcano, once home to famous mathematician Pythagoras.

A cave network located at the southernmost tip of mainland Greece was once believed to be an entrance to Hades.

Thousands of rusting train cars have been slowly falling apart on the edge of Greece's second largest city.

The ruins of an abandoned medieval city where the last Byzantine emperor was crowned.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

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

This legendary city has been a tourist attraction for centuries.

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

A spectacular cave and a beguiling lake.

The hallucinogenic center of the ancient world.

Monasteries on rock pillars, once accessible only by frayed ropes.

Dive for drinks at Croatia's first and only underwater winery.

The only gulag ever to exist in socialist Yugoslavia.

Now abandoned, the world's first torpedo factory is crumbling into the sea.

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

The complex has been abandoned since the Croatian War of Independence, barring a stint as a set for 'Game of Thrones.'

Once a state-of-the-art tuberculosis treatment spa, these ruins are now ruled by paintball players.

The remains of a sunken military ship wreck visible through clear water.

Legend has it fairies gathered at the site of this medieval castle.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

Yugoslavia's biggest underground airport lies in ruins.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

A wonderfully strange collection of 500+ stuffed frogs doing people things.

An ethereal glowing blue ocean cave in Croatia.