In 1918, a Viennese liquor manufacturer, bought the abandoned mine with the idea to an amusement establishment. Later, he tried his hand at mushroom cultivation, which, unfortunately, failed because the temperature was too low. In 1920, he had the 200-meter-long winding gallery – still largely lined with wood from the mining times – vaulted with bricks. In the early 1930s, the mine waa wired for electricity and, with an old military pontoon and an electric boat, the mine opened for tours in 1932.
During World War II this area was requisitioned by the German military because of the protection that the subterranean site offered. The original plan was to store edible fats in the tunnels, but this failed because of the high humidity. Large quantities of technical fats were stored in barrels. Cultural goods were also stored to protect them from war damage. During this time, the mine continued to operate as an exhibition mine. It was not until 1944 that the tunnels were fully confiscated and an aircraft factory was set up in them under the code name Languste. It was in this site that one of the first jet fighters in the world was produced (one of the Luftwaffe’s secret weapons).
At the end of the war only a few of the bombs previously laid by the SS were detonated during the escape because of the intervention of an Austrian sergeant. Despite this, however, there was still a great deal of damage to the mine. In 1945, the arduous process of clearing out all the equipment, machinery, and aircraft parts began. however, the sea grotto was confiscated by the Soviet occupation forces at the start of 1946. It was not until half a year later that permission was obtained to re-establish the grotto as an exhibition mine.