Eisriesenwelt Ice Cave

The world's largest ice cave, running 42 km into the Tennengebirge mountains above Werfen, with its first kilometre filled with spectacular ice formations, lit by the carbide lamps that visitors carry on the guided tour.

It's open from May to October. Reaching the cave involves a walk up, a cable car and another walk, then about 700 steps inside; allow about 3 to 4 hours in all. It's below freezing inside; bring warm clothes. Photography isn't allowed. The castle of Hohenwerfen is nearby.