British documentary series exploring incredible feats of human endeavour underground, revealing what people have built, where they have built it, how and why.
Episodes Season Season 2 · 0/10 Season 1 · 0/10 0/10 watched · 2022
S02E01 Murder Raid Tunnels 2022-01-10 45m
Exploring the extensive air raid tunnels hidden beneath Ramsgate. Also, how the former thriving mining town of Butte, Montana repurposed the 10,000 miles of tunnels. more
S02E02 Grand Canyon's Lost Treasure 2022-01-17 45m
Exploring inside the Grand Canyon Caverns - North America's largest dry cave system. Plus, Cold War radar bunkers around the UK. more
S02E03 Cincinnati's Secret Caverns 2022-01-24 45m
Exploring the forgotten underworld hiding beneath the streets of Cincinati, USA. Plus, a state-of-the-art Cold War fortress on the shores of Denmark. more
S02E04 Hotel Bunker of the Apocalypse 2022-01-31 45m
Exploring the secret, Cold War US government bunker hidden under Greenbrier Hotel, West Virginia; Plus, delve into the depths of a former slate mine in Wales, UK. more
S02E05 Mystery of the Kentucky Cave 2022-02-07 45m
Exploring the vast 400-mile Mammoth Cave in Kentucky, USA. Plus, a newly constructed opening into a metal mine in Wales - untouched for over 70 years. more
S02E06 Ireland's Underground Alcatraz 2022-02-14 45m
Exploring hidden defences that have kept Cork Harbour, in Ireland, safe for over 400 years. Plus, a former submarine base in the fjords of northern Norway. more
S02E07 Medieval Maze of Secrets 2022-02-21 45m
Exploring 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. more
S02E08 Buried Lab of the Black Hills 2022-02-28 45m
Exploring a former gold mine turned scientific laboratory in South Dakota. Plus, limestone tunnels in London and a former water cistern in Denmark. more
S02E09 Subterranean Silo Survival 2022-03-07 45m
Exploring old tunnels in an abandoned tin mine beneath the moors of Cornwall. Plus, former Atlas missile siloes in Kansas and tunnels hiding under Valetta. more
S02E10 Italy's Subterranean Secret 2022-03-14 45m
Exploring caves beneath Orvieto in Italy, originally built by the Etruscans long before the Roman Empire. Plus, a former limestone mine under Kansas City. more 
