Traces of the ice age glaciation dominate the landscape of the Lake Grimsel. Clearly visible is the border of glacier grinding tracks, where rounded granite walls and steep, sharp rock peaks meet. Here one can guess the enormous extension of the Unteraar glacier long time ago. While the high rocky peaks were sticking out of the ice, the rocks on the valley slopes were polished smooth by friction and pressure of the huge ice masses. Numerous stones, which were enclosed in the ice at the bottom of the glacier, had an effect like sandpaper.