title: Seegrotte
text: # Seegrotte
  
  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 litres 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 water level down.
  
  Visitors can tour the old mine and take a boat ride across the underground lake.
  
  ## World War II history
  
  During World War II the Seegrotte was used for production of Heinkel He 162A jet fighters in Nazi Germany's "second Ruhr".
  
  