A massive cave once a secret military base is now home to thousands of bats.

The site of many battles and tragedies, including the 40 maidens who leapt into the sea.

A striking symbol of the Bulgarian capital.

An abandoned saucer-shaped monument in the Bulgarian mountains.

This historic timepiece is thought to be the only public clock in the world that keeps lunar time.

The world's most important buildings shrunk to a tiny size.

Austria's ultra-modern art museum looks like Cthulhu's giant alien heart.

Resting in the middle of an Austrian river, this sci-fi "island" lets people cross in neon style.

A neo-Gothic church built to thank God for saving the Emperor of Austria from an assassination.

Op-art architecture designed for happiness.

A beautiful modern church dedicated to the teleporting patron saint of Andorra.

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

A whimsical bridge adorned with decorative dragons.

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

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

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

The bust of Romania’s most notorious ruler, Vlad Dracula aka "Vlad the Impaler," keeps watch over the ruins of his medieval court.

After sitting unused for decades, this abandoned communist infrastructure became a wildlife utopia.