One of the largest caves in the world open to the public.

This Roman monument is surrounded by more recent construction, offering a stark contrast between ancient architecture and the modern urban landscape.

One of the tallest lighthouses in the world also serves as a monument to the fallen of World War I.

A whimsical bridge adorned with decorative dragons.

This abandoned Slovenian military barracks has become a punky-political art squat.

This one-time health resort was used by aristocrats around the world.

This massive subterranean fissure is known as the "underground Grand Canyon."

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

This exceptional home was a 32-year labor of love by a man determined to build his wife the most beautiful stone house in the world.