The tallest mountain in mainland Netherlands isn't actually very tall.

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

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

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

No shoes allowed on this trail, which is designed to be experienced barefoot.

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

Incredible labyrinth of man made caves.

This centuries-old gothic monster has been converted into a sprawling, glossy bookstore.