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

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

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

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

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

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

Where the lovelorn find a home for their sentimental keepsakes.

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

An ethereal glowing blue ocean cave in Croatia.

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

This abandoned airplane hanger is said to have once been a top secret launch facility.

A bridge destroyed three times: once as a ruse, then in an actual attack, and finally for the movies.

This abandoned Olympic skiing facility still bears the scars of the Siege of Sarajevo.

A former bank seized as a sniper vantage point during the Bosnian War is now a secret graffiti art gallery.

This historic cemetery was inaccessible for several years due to dozens of land mines.

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

The haunting ruins of a military fortress turned astronomical observatory sit on a Sarajevo mountaintop.

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

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

Yugoslavia's biggest underground airport lies in ruins.

Bridge that died in war and was resurected.

Bronzes and busts that once stood in the city's main squares are now relegated to a small hidden courtyard.

This ominous Albanian fortress houses tanks and downed planes as a reminder of their victories over Western imperialism.

The elliptical citadel resisted the advance of the mighty Ottomans several times, thanks to the military prowess of the "Dragon of Albania."