This beautiful natural train tunnel is said to grant the wishes of visiting lovebirds.

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

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

A whimsical bridge adorned with decorative dragons.

Martin Bricelj Baraga's monolithic sculpture measures the blueness of the sky, and changes color to match it.

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

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

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

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

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

Where the lovelorn find a home for their sentimental keepsakes.

Yugoslavia's biggest underground airport lies in ruins.

This stunning, out-of-the-way Croatian monument commemorates a community's uprising against occupying fascist forces.

A musical instrument played by the sea.

An ethereal glowing blue ocean cave in Croatia.

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

This cluster of little wooden huts once ground local farmers’ wheat into flour during the days of the Austro-Hungarian Empire.

These warring psychedelic crags commemorate an unsuccessful military operation.

This top-secret nuclear bunker hidden in a Bosnian mountain has been converted to a modern art exhibition space.

This museum preserves the hand-dug tunnel that kept Sarajevo afloat during the Serbian siege.

A war-torn Olympic relic is being overtaken by graffiti and nature.

Bridge that died in war and was resurected.

There's a mini version of Iguazu Falls hidden in the Balkans, and it's got a rope swing.

Every year, the town of Menton, France, turns lemons and oranges into giant sculptures depicting windmills, dragons, and more.