The Eisriesenwelt is a natural limestone and ice cave located in Werfen, Austria, about 40 km south of Salzburg. The cave is inside the Hochkogel mountain in the Tennengebirge section of the Alps. It is the largest ice cave in the world, extending more than 42 km and visited by about 200,000 tourists every year.
The Tennengebirge mountains were formed during the late Tertiary period, during the Würm glaciation period of the Pleistocene. The mountain range, one of the massifs in the Austrian Alps, is the largest karst plateau in the Salzburger Alps, and the Eisriesenwelt is located at the rim of this plateau. Although the cave has a length of 42 km, only the first kilometer, the area that tourists are allowed to visit, is covered in ice. The rest of the cave is formed of limestone.