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

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

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

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

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

The only gulag ever to exist in socialist Yugoslavia.

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

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.

A World War II evacuation tunnel turned into a history display of Croatian state and people.

This former estate of a fascist leader is now a burnt out ruin leading to a system of secret tunnels.

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

Where the lovelorn find a home for their sentimental keepsakes.

An ethereal glowing blue ocean cave in Croatia.

A whimsical bridge adorned with decorative dragons.

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

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

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

Historic house-museum dedicated to the revolutionary gay graphic artist Tom of Finland.

The island houses the ruins of a secret nuclear fusion lab that once employed high-profile Nazi scientists

105-foot wide giant metallic flower blooms anew every day in the heart of Buenos Aires.

With its vast selection of books, comics, and records, this nearly 70-year-old open-air market always rewards the patient browser.

A shrine of fire worship built on top of a natural flame.

Mysterious hillside with a continuously burning natural fire.