In the Dolomites, more particularly in the Brenta Group in the south of Bozen, there is a cave, which houses an extraordinary water phenomena, the so-called “Bus della Spia” (Cave of the Spy). Inside the mountain, the water level rises and falls periodically up to 13 meters, very similar to the tides in the sea. The reasons are unknown. The cave scientist Thomas Hofer wants to dive to end of the cave in order to find out, where the water is coming from and where it is flowing to. All expeditions of Thomas Hofer bring him to places, where no human has been before.