Hölloch Cave

The Hölloch (English: Hellhole) is a 211.2 km (131.2 mi) long cave in the municipality Muotathal in Switzerland. In addition to being the third longest cave in Europe and the 11th longest in the world, it is also notable for having a depth of 1,033 m (3, 389 ft). The Hölloch is an example of a karst cave system.