Erosion caused the mountain to collapse and the vast, pale yellow and reddish rock basin to form, which becomes bigger every year. From the Grabenrad or the Illhorn (2,716 m) there are "fear inspiring" yet stunning views down into the Rhone valley.
The alpine route connecting Braunwald to Lake Oberblegi and down to Schwanden leads hikers through the weird rock formations of the moranes of the Glaernisch Range. Indeed, the deep-blue lake itself was created by moranes that dammed the melting waters. Rushing mountain streams and beautiful alpine flowers round off the picture.