About this season
Historians, engineers, and experts take a look at the underground structures, systems, and phenomena that exist beneath our feet.
Episodes (10)
1. Secrets of the Rock
Aired 17 October 2019 • 45 min
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 reveal the secrets of a long-lost chamber with evidence of high-stakes espionage.
2. Mystery of the Lost Labyrinth
Aired 24 October 2019 • 45 min
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 excavation into this mysterious 9,000-foot tunnel system might finally reveal its dark secrets.
3. Secrets of the Terror Tunnels
Aired 31 October 2019 • 45 min
A vast system of tunnels built almost three thousand years ago was the site of the greatest battles of antiquity, and these disorienting passages could be the deadliest weapon in war; experts reveal what made this underground world so terrifying.
4. The Renegade's Lair
Aired 7 November 2019 • 45 min
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 he left here to discover new parts of this mysterious network.
5. Cave of the Body Snatchers
Aired 14 November 2019 • 45 min
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 excavating these rubble-filled caves to reveal the secrets of what these bandits left behind.
6. World's Biggest Labyrinth
Aired 21 November 2019 • 45 min
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 place reveal the long-lost secrets of Nazi occupation, Soviet revolution, and Cold War subterfuge.
7. Treasures of the Lost Mine
Aired 5 December 2019 • 45 min
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-edge tech to follow rumors of a mysterious long-lost mine in search of a payday.
8. Ghosts of the Hell Maze
Aired 12 December 2019 • 45 min
A labyrinth of tunnels in the French countryside has served as a secret hideout during wartime for centuries. On its walls, experts have discovered the final confessions of soldiers who fought here during one of the deadliest days of World War I.
9. Conspiracy in the Buried City
Aired 19 December 2019 • 45 min
A buried ancient city hidden five stories underground, and to keep its location secret from invaders, its residents devised an ingenious trick; experts reveal what it was, and using the latest tech, they reveal the truth behind this strange place.
10. Curse of Cannibal Caves
Aired 26 December 2019 • 45 min
A mysterious cave system is home to some of the oldest human remains ever discovered, and today, the explorers and researchers investigating this site are uncovering shocking evidence of cannibalism among its Ice Age denizens.