Hölloch Cave is a 197 kilometres (122 mi) long cave situated between the river Muota and the area of the Pragelpass in the Valley of Muotha in Switzerland. It is also notable for having a depth of 939 metres (3,081 ft) and being the second longest cave in Europe.[1] The initial exploration started in 1875 and was led by Alois Ulrich. A large part of the exploration of this cave was led by Alfred Bögli. The explored length of the cave increased from 25 kilometers (16 mi) in 1952 to 100 kilometres (62 mi) in 1968 (it was the first cave in the world where the explored length reached 100 km). Until 1970, it was thought to be the largest cave complex in the world, this title now held by Mammoth Cave.[1]