One of the best-preserved Roman amphitheaters is still used today, but for less brutal events.

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

The only gulag ever to exist in socialist Yugoslavia.

A tower marking the spot where Yugoslavia began its resistance against the invading Nazis stands neglected, but not quite forgotten.

Croatia's "hairy stone" fortress is one of the most well preserved Istrian castles.

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

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

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

This huge metal monument is slowly being stripped to its concrete skeleton.

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.

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

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

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

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.

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.

A garden of flying flowers.

You would never come across this tiny green oasis if you didn't know it existed.

Ancient man-made caves underneath small town Belgium.

The vast chamber inside this abandoned cooling tower looks like something out of a sci-fi dystopia.