The elliptical citadel resisted the advance of the mighty Ottomans several times, thanks to the military prowess of the "Dragon of Albania."

An Albanian monument to the Communism that nearly crushed the country is now a crumbling wreck.

The largest Roman amphitheater in the Balkans once held over 20,000 people, but managed to lay hidden for hundreds of years.

A medieval bridge stretches over a sulfur-rich river that leads to year-round natural hot springs.

This ominous Albanian fortress houses tanks and downed planes as a reminder of their victories over Western imperialism.

A naturally beautiful, seemingly bottomless deep blue spring.

Five candy-colored villages on the Italian Riviera.

The bomb-ravaged remains of of a colossal Neptune.

This former fascist summer camp was abandoned for decades.

A sunken idol welcomes parishioners to Davy Jones' Locker.

Remote, beautiful, and stigmatized, Las Hurdes is Spain's version of Appalachia.

This French ghost town from World War II has been left as a memorial to German atrocities during World War II.

This former limestone quarry is now a subterranean wonderland of grand stonework.

A garden of massive sculptures sits in Jean Lindard's backyard.

An atmospheric, medieval-themed book store hides in a 13th-century underground space.

Hundreds of dwarf beeches create an unusual, haunting forest in the north of France.

A swath of France so devastated by war it is still forbidden to go there.

This modern French ossuary contains the jumbled bones of 130,000 WWI soldiers.

Once the local rulers had gone these enchanting ruins housed common folk in an almost real life fairy tale.

Hiding the longest subterranean river known in the world.

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

The highest point in Belgium is a staircase to nowhere.

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

This mine is home to the largest man-made hole in Europe.