The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

Replicas of Apollo's leonine stone guard cats still line a sacred row in Greece.

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

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

A Bronze age settlement on the Greek island of Santorini might have been the inspiration for Plato's Atlantis.

Giant marble phalluses on the sacred island of antiquity.

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

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

This 600-year-old home seems to defy physics.

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

A collection of artworks exclusively created by the mentally ill that was almost burned by Nazi culture police.

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

This modern arts center is built around a gem of late-Baroque architecture.

This Greek temple, open only an hour a day, was the site of a war of tastes between an architect and an artist.

This former Masonic lodge has been transformed into part museum, part bar, all awesome.

This ghost town in Belgium will lose its street art when it ceases to exist.

Sky ships, planes, and portraits left as unique tokens of hope and thankfulness.

A crumbling island fortress that seems to be covered in a field of stone crosses but is simply incomplete.

What if all public housing projects had been designed by "the Pygmalion of modern architecture," not only their prototype?

Miles of man-made caves and tunnels are currently used for cultivating mushrooms.

First museum dedicated to the research and history of Epilepsy.

This collection of French root art looks like an indoor fairy wonderland.

This series of Baroque passageways in Vienna's cultural center mix old architecture with modern art.

Apartment complexes built into huge repurposed natural gas tanks.