A hidden, subterranean city built within the Rock of Gibraltar was an immense fortress to control the seas during Wor...

A strange, centuries-old labyrinth built into an abandoned quarry was built by an eccentric millionaire, and no one k...

A vast system of tunnels built almost three thousand years ago was the site of the greatest battles of antiquity, and...

A strange underground system known as the Black Cave was home to an infamous nobleman on the run from the law; today,...

An eerie system of underground vaults in Scotland was once the hideout for thieves who stole newly-buried bodies and ...

The world's biggest labyrinth is a 1,553-mile cave system that's home to some of history's darkest mysteries, and new...

Caverns hidden deep inside a remote mountain are home to a precious mineral found nowhere else on earth, and experts ...

A labyrinth of tunnels in the French countryside has served as a secret hideout during wartime for centuries. On its ...

A buried ancient city hidden five stories underground, and to keep its location secret from invaders, its residents d...

A mysterious cave system is home to some of the oldest human remains ever discovered, and today, the explorers and re...