The accidental flooding in 1912 resulted in over 20 million liters of water filling the lower mine levels.
The underground lake is created by a constant natural spring that maintains the water level.
During WWII, the facility utilized forced laborers to excavate and expand the tunnels for aircraft production.
The Heinkel He 162, a Nazi 'wonder weapon' jet fighter, was assembled inside the caverns to protect production from Allied aerial bombings.
A portion of the 1993 film 'The Three Musketeers' was filmed on location inside the mine.
The mine includes a memorial chapel dedicated to the miners and those who lost their lives during the war era.
The air inside the mine is considered very clean and free from pollen, sometimes used in historical therapeutic contexts.
Seegrotte is a former gypsum mine in Hinterbrühl, Austria, featuring the largest subterranean lake in Europe. The site was flooded in 1912 after a blasting accident triggered a massive inflow of water. During World War II, the facility was repurposed by the German Luftwaffe to manufacture Heinkel He 162 jet fighters in the dry sections of the tunnels. Visitors navigate the labyrinthine tunnels and the 6,200-square-meter underground lake via guided boat tours. The temperature inside the mine remains constant at approximately 9 degrees Celsius throughout the year. The site preserves remnants of both its industrial mining past and its specialized wartime aircraft assembly history. It is situated within the Vienna Woods region, approximately 20 kilometers south of Vienna.
The central boat dock where the scale of the subterranean lake is most clearly visible against the rock walls.
Bring a warm jacket regardless of the outside weather, as the cave temperature is consistently cold.
Wear comfortable, non-slip footwear as the ground inside the mine can be damp and uneven.
Allow for extra time if visiting on a weekend during the summer, as the boat tours operate on a first-come, first-served basis.
Do not arrive without a jacket, as the transition from hot summer air to the cool, damp cave environment can cause thermal discomfort.
Open daily throughout the year, but subject to occasional maintenance closures for safety inspections.
No flash photography is allowed inside the cave. Stay with your assigned tour group at all times.
