Mysterious craters may have been home to an ancient cult.

The ruins of an Estonian prison are drowning in the quarry lake where the convicts were once forced to work.

"There's nothing there," and other lies the KGB told us.

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

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

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

This heart-shaped island looks substantially less lovely after a recent bulldozing project.

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

A full figure 4th century incorruptible saint lies in a glass coffin in Croatia.

An eclectic art form practiced by untrained masters is celebrated at this museum in the heart of Zagreb's old Upper Town.

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

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

The only gulag ever to exist in socialist Yugoslavia.

Croatia's towering concrete blossom grows from the site of a World War II concentration camp.

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.

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

This scale model of our solar system hid in plain sight for years before a physics team sought out all the planets.

Gargoyle head that brings good luck.

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.

Humble beginnings for one of the world's most famous scientists.

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