The Seegrotte, formed by an abandoned gypsum mine in the Austrian town of Hinterbrühl, consists of a series of underground canals forming the largest underground lake in Europe. And, the same cause that led to the closure of the mine, is the one that created the lake; the flooding of the caves.
In 1912 a detonation in the Hinterbrühl chalk mine, just 20 kilometres from Vienna, went wrong, causing the mine to flood completely and a lake to form. At about 60 meters below ground level, the lake has an area of 6,200 square meters and has to be emptied every day, because the water does not completely flood the caves. During the Second World War, the caves were also heavily bombed by Allied aircraft, because the upper levels of the caves were used to build German army airplanes.
