Ancient man-made caves underneath small town Belgium.

The "stairway to heaven" lookout tower was built to resist weather, arson, and the laws of physics.

Sculpture designed by Turkish artist and professor Mehmet Ali Uysal.

This abandoned Belgian fortress is purposefully being left to nature.

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.

Incredible labyrinth of man made caves.

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

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

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

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.

The names Lúthien and Beren can be found inscribed on the shared grave of the famous writer and his beloved wife and muse.