Kaisergebirge Run (38,5km)

Difficulty depends on your fitness level, of course, but for me it was the biggest running achievement I´ve ever done. So far. Good thing is that you can get supply of water within reasonable distances from the springs (Petersbrünnl, Kaindlhütte, Hans-Berger-Haus, Stripsenjochhaus → have to pay, Hochalm → spring was dry, Ritzaualm). Due to dry springs and high temperature, it is recommended to run earlier after the winter.