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

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

This beautiful Croatian fortress is haunted by legends of forbidden love.

A tribute to an iconic act of defiance from the Croatian War of Independence involving a small car.

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

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

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

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

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

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.

A forgotten and crumbling Yugoslav monument to the victims of fascism.

Over time, this castle grew to encompass the entire island.

The first museum dedicated to exploring humanity's cultural relationship with the celestial world.

An old hill fort covered in over 100,000 crosses is a symbol of Lithuanian nationalism and beliefs.

A memorial to the murdered Jews of Kaunas.

Open-air museum with a large collection of Soviet-era statues.

These massive moving sand dunes have swallowed an entire village and are still on the run.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

These 17th-century mummies are no longer naturally preserved, but remain on display today.

An enormous and lavish Gothic church in Czechia.

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

Underneath this small church are 15,000 bones, arranged by an obsessive academic.

Two monstrous faces loom over a village in Czechia.