Underground Marvels

A hidden, subterranean city built within the Rock of Gibraltar was an immense fortress to control the seas during World War II, and new discoveries re...

A strange, centuries-old labyrinth built into an abandoned quarry was built by an eccentric millionaire, and no one knows why; but now, a new excavati...

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

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

An eerie system of underground vaults in Scotland was once the hideout for thieves who stole newly-buried bodies and sold them; today, experts are exc...

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

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

A labyrinth of tunnels in the French countryside has served as a secret hideout during wartime for centuries. On its walls, experts have discovered th...

A buried ancient city hidden five stories underground, and to keep its location secret from invaders, its residents devised an ingenious trick; expert...

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