Seegrotte Hinterbrühl

The Seegrotte lies near Hinterbrühl in Lower Austria, a cave system beneath a former gypsum mine. The mine flooded in 1912 with twenty million litres of water, creating an underground lake. The water surface covers 6,200 square metres sixty metres below ground. Pumps keep the level low so visitors can enter safely. The site reopened as a tourist attraction after 1930 and has operated almost continuously since, except during the Second World War. During the war the Seegrotte became a secret factory for Heinkel He 162A jet fighters. The aircraft were assembled underground to avoid Allied bombing raids. Production lines ran inside the cave, using forced labour under harsh conditions. After the war the site returned to tourism, preserving traces of its wartime past. Visitors walk through old mine tunnels and board small boats for a ride on the underground lake. The grotto’s high vaulted chambers and still water create an unusual setting. Guides point out wartime machinery left in place. The cool air and echoes add to the atmosphere of a place shaped by both mining and history.