The Achensee - lake Achen - is the largest lake in Tyrol. It is 9,4 km long and at its widest point 1000 m wide and at its deepest part 133 m deep. The lake originated after the last Ice Age. The water in the lake is so pure that its quality is said to be that of drink water.

There is a small seperate pool at this end of the lake and here the water temperature is much warmer than in the rest of the lake - at the moment approx. 14°