The Seegrotte show mine in Hinterbrühl is a disused gypsum mine with mythical-looking tunnels, a mine or barbara museum and the largest underground lake in Europe.
The Seegrotte is a former gypsum mine in the Lower Austrian market town of Hinterbrühl, about 15 km south of Vienna, which today - as from 1932 - serves as a show mine. Seven springs feed the largest underground lake in Europe, covering 6200 m². He has no natural drain.