The highest point in Belgium is a staircase to nowhere.

An early 20th-century sanatorium, long abandoned and now being reclaimed by nature.

Hiding the longest subterranean river known in the world.

A former customs station on the border of Germany and the Netherlands.

A top-secret bunker now turned museum, is an eerie look at what life would have looked like in the event of nuclear war.

This German art chapel is perfect for those who like their worship hard, modern, and utterly alien.

This former Nazi castle was built as a school to train what would have been the future of the Third Reich.

Its town washed away centuries ago, this lonely tower by the sea tells the tale of a mermaid and a curse.

Watch the local Netherlands birds from inside this giant eco-egg.

This medieval castle was painted pink as part of a now-abandoned children's theme park.

This fairy tale forest hides scenes from some of the more obscure and bizarre Western nursery stories.

Inspired by "The Starry Night" this Dutch bike path turns into a glowing work of art each night.

This massive collection of taxidermy is full of specimens collected by missionaries during their international travels.

Two gravestones clasp hands over the religious divide.

A luxury hotel housed in a former 15th century Gothic church.

This historical Netherlands fortress still bears the marks of its single siege.

Incredible labyrinth of man made caves.

This sprawling Belgian fort was once thought of as impenetrable but now it is simply an abandoned relic.

A Belgian self-built tower inspired by the Bible and ancient civilizations.

Descend into the tunnels to experience the life of a coal miner.

The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

Visit the ancient, mysterious Roman catacombs ... in the Netherlands.

Abandoned since 1998, this train station has become an oasis for urban explorers.

This bakery and museum offers tours of the tastes and mythology of Aachen's signature spice biscuit—just don't ask for the recipe.