In this episode we head a mile underground in the Black Hills of Dakota, to the lowest level of a former gold mine that has been converted into Sanford Underground Research Facility, one of the world’s leading scientific research stations. The ultra deep location provides sufficient quiet from background radiation to allow scientists to hunt for elusive neutrinos.
We visit a huge network of limestone tunnels under a quiet London suburb. The man made caverns have a long and varied history, playing host over the centuries to druids, medieval miners, bomb shelter residents and World War 2 double agents.
And we venture into the darkness of a former middle ages water cistern, built to protect the residents of Copenhagen from a deadly cholera outbreak. The huge caverns are now home to a very different experience.
