A church of bones, decorated with 40,000 human skeletons.

Now harmless, this looming post struck fear into the heart of medieval troublemakers.

The Renaissance-era courthouse is a relic from the fortified town's centuries of Venetian rule.

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

Colorful concentric circles honor a small Croatian town's supposed spot at the nucleus of it all.

An ancient knight and a symbol of the city's freedom.

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

This abandoned Croatian stronghold never saw a great deal of conflict but it is still a beloved relic nonetheless.

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

When Croatia became independent of Yugoslavia, the splintering governments left behind these concrete tunnels.

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

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

A wunderkammer of gold and silver reliquaries and ancient saintly bones.

Longest fortress system anywhere in Europe.

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

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

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

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

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

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.

One of Belgium's oldest hospitals saw patients from the 13th to 20th centuries before becoming a museum.

The foundations of a forgotten fortress, wedged in between two streams.

A taxus-tree to which Julius Caesar reputedly tied his horse.