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The top-secret construction of a massive nuclear bunker remained concealed under a palatial West Virginia hotel for decades; experts reveal how this vast subterranean structure was one of the most closely guarded Cold War secrets in U.S. history.
Deep beneath the streets of Cincinnati lies a network of deserted tunnels and caverns that contain a remarkable history of the city's origins, and now, experts investigate to reveal who built this underground labyrinth and why it was abandoned.
Hidden beneath the town of Ramsgate, England, lies a hidden network of over three miles of air raid tunnels; experts investigate and uncover an extensive WWII bomb shelter that became a permanent refuge for many civilians after a devastating attack.
The longest known cave system in the world spans hundreds of miles beneath the hills of Kentucky, and containing prehistoric artifacts and ancient human remains, experts reveal a subterranean mystery that may have changed the course of U.S. history.
Buried nearly a mile beneath the Black Hills of South Dakota is a cutting-edge laboratory at the forefront of astonishing scientific research; experts reveal advancements engineers achieved more than a century ago that keep it operating today.
A decommissioned missile launch facility in Kansas remained one of the best kept subterranean military secrets of the Cold War; experts reveal how this abandoned underground complex transformed into a state-of-the-art survival bunker.
Descending more than 200 feet beneath the Arizona bedrock lies the largest dry cave system in North America, and now, experts explore this vast subterranean network to reveal the mysteries and undiscovered treasure that remain hidden within its walls.
Subterranean military fortresses situated on the southern coast of Ireland have protected against enemy invasion for over 400 years, and now, experts investigate how this powerful stronghold transformed into a brutal and terrifying prison.
A forgotten world of ancient underground passages and medieval engineering lies hidden beneath the town of Exeter, England; experts investigate and reveal how this ambitious tunnel system was the result of one of the deadliest epidemics in history.
A hidden, subterranean city built within the Rock of Gibraltar is an immense fortress to control the seas during World War II; new discoveries reveal the secrets of a long-lost chamber with evidence of high-stakes espionage.
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.
A vast system of tunnels built almost 3,000 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.
A strange underground system known as the Black Cave is connected to a fairytale castle and was home to an infamous nobleman on the run from the law; experts investigate the secrets he left here to discover new parts of this mysterious network.
Eerie system of underground vaults in Scotland was once hideout for thieves who stole newly-buried bodies and sold them; experts excavate these rubble-filled caves to reveal the secrets of what these bandits left behind.
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.
Caverns hidden deep inside a remote mountain are home to a precious mineral found nowhere else on Earth; experts and treasure hunters use cutting-edge technology to follow rumors of a mysterious long-lost mine in search of a payday.
A labyrinth of vast tunnels in the French countryside has served as a secret hideout during wartime for centuries, and on its walls, experts have discovered the final confessions of soldiers who fought during one of the deadliest days of World War I.
A buried ancient city hidden five-stories underground can house 3,000 people in secret; experts use the latest tech to reveal the truth behind this strange place.
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.