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

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

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

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

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

Bridge that died in war and was resurected.

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

This picturesque monastery at the base of a cliff is a peaceful oasis open to all visitors.

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

An ethereal glowing blue ocean cave in Croatia.

Built as an anti-fascist tribute, this surreal Yugoslav memorial became an unwelcome symbol after the Croatian war for independence.

Legend has it fairies gathered at the site of this medieval castle.

Now abandoned, the world's first torpedo factory is crumbling into the sea.

This military tunnel dates back to World War II and provides visitors with a little wartime adrenaline.

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

Yugoslavia's biggest underground airport lies in ruins.

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

This unique structure allowed boats to bypass underwater mine barriers in the channel to enter the harbor.

This picturesque medieval monastery guards a small trove of historic treasures.

Dive for drinks at Croatia's first and only underwater winery.

Longest fortress system anywhere in Europe.

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

The now-overgrown beach resort was once frequented by Yugoslav military elite.

According to a local legend, this old castle could only be built after a woman was immured in the walls.