Eisriesenwelt

The largest ice cave in the world, inside the Hochkogel in the Tennengebirge, running more than forty-two kilometres and taking about 200,000 visitors a year. Only the first kilometre, the part open to tourists, is covered in ice; the rest is limestone. The Salzach eroded the passages, and the ice formed from thawing snow that drained in and froze. Because the entrance stands open all year, cold winter winds blow in and freeze the snow inside, and in summer a cold draught out of the cave holds it.