Exploring the secret, Cold War US government bunker hidden under Greenbrier Hotel, West Virginia. Plus, delving into the depths of a former slate mine in Wales.
Mysterious caverns in the city of Cincinnati are examined. A network of cellars, wells and tunnels in Cincinnati that were used to create the world's most popular beer. Plus, a state-of-the-art Cold War fortress on the shores of Denmark.
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.
Exploring hidden defences that have kept Cork Harbour, in Ireland, safe for over 400 years. How did this powerful stronghold became a brutal and terrifying prison. Plus, a former submarine base in the fjords of northern Norway.
A decommissioned missile launch facility in Kansas remained one of the best kept subterranean military secrets of the Cold War, and now, experts reveal how this abandoned underground complex transformed into a state-of-the-art survival bunker.
Exploring the maze of of long narrow tunnels beneath Exeter that were built in medieval times to protect the city. Plus, a marble quarry under the pine forests of Vermont.