Aletsch Glacier, the largest glacier in the Alps, covers more than 120 square km in southern Switzerland. It descends round the south of the Jungfrau into the valley of the Upper Rhône; at its eastern extremity lies a glacier lake, Lake Märjelen (2,350 meters above sea level). To the west rises Aletschhorn (4,195 meters), which was first climbed in 1859. The Rhône River flows along the southern flank of the mountains. It has recently been designated a UNESCO world heritage site, in recognition of its importance and uniqueness.
