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 of 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.

The cave was first scientifically explored in 1875 by a group led by Alois Ulrich. Later expeditions in the 1950s by Alfred Bögli, one of the pioneers of speleology, managed to explore a large part of the cave.

The explored length of the cave increased from 25 km (16 mi) in 1952 to 100 km (62 mi) by 1968.