The Seegrotte (Lake Grotto) in Hinterbrühl, Austria, is home to the largest underground lake in Europe — a surreal subterranean body of crystal-clear water, 60 metres below ground, formed when a gypsum mine flooded in 1912 and creating a spectacular underground world where visitors can glide across the lake’s surface by electric boat through vast, still caverns of extraordinary atmospheric power. Located just 17 kilometres south of Vienna, the Seegrotte is one of the most unusual day trips from the Austrian capital — part industrial heritage (the gypsum mining history), part geological wonder, and part World War II history (the Nazis used the flooded mine as a secret aircraft factory, building Heinkel He 162 jet fighters here using forced labour from Mauthausen concentration camp).

Quick Facts: Seegrotte, Austria

• Best time to visit: Year-round — the underground temperature is a constant 9°C regardless of the season; bring a warm layer even in summer; the lake is especially atmospheric when the cave’s lighting reflects on the still water
• How to get there: ~25 minutes from Vienna by car (A21 motorway towards Hinterbrühl); ~45 minutes by public transport (Vienna S-Bahn to Mödling + bus); the Seegrotte is in the village of Hinterbrühl
• Entry fee: ~€12 (adult) including the boat ride on the underground lake
• Lake size: 6,200 m² — the largest subterranean lake in Europe

Not far from Vienna, in the village of Hinterbrül, there is the cave system with the largest underground lake in Europe – Seegrotte, covering an area of 6,200 m². It is not a classic natural cave but the former gypsum mine. In 1912, the ceiling fell down and mine was flooded with 20 million liters of water.

Photo by seegrotte.com

In the past, up to 1800, the cave was used for making red and white plaster. During World War II the cave housed also the factory for the production of combat aircraft. The first jet fighter in the world (Heinkel He162) was constructed right here.

The underground lake was explored in the 30′s of last century, and later open to the public. There are 9 °C in the cave and the tour lasting 45 minutes includes a boat trip. Seegrotte is now great tourist attraction with about 250,000 visitors a year. It is open every day, all year-round. The basic adult admission is €9 or €6 for children.

Open:
1st April – 31 October from 9.00 to 17.00
1st November – 31 March from 9.00 – 12.00 and 13.00 – 15.00

Seegrotte is one of the most impressive natural attractions in the world. Being also a cultural monument it should be definitely included in your list of places to visit when travelling to Austria.

For further information visit Seegrotte official site.

View The Hinterbrühl Seegrotte in Austria in a larger map

Have you taken the boat across Europe’s largest underground lake or explored the Seegrotte near Vienna? Share your subterranean Austrian adventures in the comments! 🛶

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