The Seegrotte, near Hinterbrühl, Austria, is a cave system with a large grotto located under a former gypsum mine.
It was closed in 1912 after the mine flooded with 20 million liters of water. It became a tourist attraction after 1930 and has been one ever since, with the exception of World War II. The lake is 60 meters below ground, the water surface is 6200 m² and pumps are used to keep the waterlevel down.Visitors can tour the old mine and take a boat ride across the underground lake.
Wikipedia https://en.wikipedia.org/wiki/Seegrotte
Address 2 Grutschgasse, Hinterbrühl 2371, Austria
Coordinates 48°5'9.823" N 16°15'26.37" E
