Underground Worlds

Explores the extensive air raid tunnels hidden beneath Ramsgate, and how the former thriving mining town of Butte, Montana, repurposed the 16,000km of tunnels.

Explores inside the Grand Canyon Caverns, North America's largest dry cave system, and Cold War radar bunkers around the UK.

Explores the forgotten underworld hiding beneath the streets of Cincinnati, USA, and a state-of-the-art Cold War fortress on the shores of Denmark.

Explores the top-secret, Cold War-era US government bunker hidden beneath the Greenbrier Hotel in White Sulphur Springs, West Virginia.

Footage of an exploration of the vast 644km Mammoth Cave in Kentucky, USA; a newly constructed opening into a metal mine in Wales that has lain untouched for over 70 years.

Explores hidden defences that have kept Cork Harbour, in Ireland, safe for over 400 years; a former submarine base in the fjords of northern Norway.

Explores long narrow tunnels beneath Exeter that were built in medieval times to protect the city; marble quarry under the pine forests of Vermont.

A former gold mine turned scientific laboratory in South Dakota, USA; some interesting limestone tunnels in London; a former water cistern in Denmark.

An exploration of old tunnels in an abandoned tin mine beneath the moors of Cornwall; former Atlas missile silos in Kansas now used by survivalists.

An exploration of the caves beneath Orvieto in Italy, that were originally built by the Etruscans, long before the time of the Roman Empire.