Mount Petzen in the Austrian-Slovenian border area houses in its interior mine tunnels of a total of several hundred kilometers in length. After the mine operation ceased in the sixties and the water was no longer pumped out, some of the lower mining horizons were flooded, creating underground lakes with crystal clear water about 8 degree Celsius. In December 2018 I swam there and will offer this adventure from 2019 as part of guided tours to other Wildswimming friends.
