What looks like a normal building is really a hollow facade hiding a subway vent.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

A museum of carnival attractions where you are invited to ride the rides.

A unique two-level bridge designed to honor a king.

This huge metal monument is slowly being stripped to its concrete skeleton.

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

This Croatian fairytale castle is slowly falling apart thanks to years of neglect.

Colorful concentric circles honor a small Croatian town's supposed spot at the nucleus of it all.

Gigantic mosaic sculptures of the figures on Tarot cards fill this colorful Tuscan garden.

Italian cave with exceptional acoustics and an unsavory history.

This small but lovely sinkhole lake is the last remnant of a great prehistoric water basin.

The oldest botanical garden in the world that technically isn't the oldest.

Erotic art covers the walls of the largest ancient pleasure palace.

Ancient snack bar of the Roman Empire re-opened.

The world's most active stratovolcano is almost always erupting.

A trough of 700 strange bronze faces runs through a narrow alley in Ljubljana's old town.

The "dragon babies" of southeastern Europe.

A whimsical bridge adorned with decorative dragons.

This abandoned Slovenian military barracks has become a punky-political art squat.

A miniature train-ride through Slovenia's largest cave system.

This one-time health resort was used by aristocrats around the world.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

The big toe of this towering monument to a Croatian national hero is worn from years of superstitious rubbing.