8.Hoelloch · Switzerland · Schwyz Muotatal image by jochen Hölloch Cave is a 198.19 kilometres (123.15 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 938.6 metres (3,079 ft) and being the second longest cave in Europe.[...] http://en.wikipedia.org/wiki/H%C3%B6lloch_Cave