The Wyssa is the highest, most beautiful but also most dangerous bisse of the 10 irrigation channels in the Gredetsch valley. Today it serves exclusively as a spectacular Suonen trail because the water flows through a tunnel toward Mund. The course is beautiful, dizzying passages alternate with 15 low and small tunnels where you have to walk on your knees on a wooden board which is placed in the bisse. A flashlight is not necessary since the tunnels are all rather short. The construction of 7 km long Wyssa-Suone is dated before 1462. It is difficult to imagine the tremendous work that was necessary for its construction and maintenance!