Under lush Alpine pastures there exists a different world. Eternal darkness, dripstones and mystic water ways which extend several kilometres into the heart of the mountains. In 2016/17, a scientific expedition tries to find and map the last still unknown connections of the deep cave system in the Ario caldera in the Spanish Picos de Europa Mountains.
At the forefront, the cave divers, daringly advance into the unknown, diving down into deep sumps where rescue from the outside is not an option.