The Aletsch Glacier or Great Aletsch Glacier is the largest glacier in the Alps. It has a length of about 23 km (14 mi) and covers more than 120 square kilometres (46 sq mi) in the eastern Bernese Alps in the Swiss canton of Valais. The Aletsch Glacier is composed by three smaller glaciers converging at Concordia, where its thickness is estimated to be near 1 km (3,300 ft). It then continues towards the Rhone valley before giving birth to the Massa River.
The whole area, including other glaciers is part of the Jungfrau-Aletsch Protected Area, which was declared a UNESCO World Heritage site in 2001.
The area of the Aletsch Glacier and some surrounding valleys is on the UNESCO World Heritage list, thus it is protected and the facilities are mostly restricted the external zones. The region between Belalp, Riederalp and Bettmeralp (which is called Aletsch Region) in Valais gives access to the lower part of the glacier. The Bettmerhorn and Eggishorn are popular view points and are accessible by cable car. The Massa river can be crossed since 2008 by a suspension bridge, thus allowing hikes between the left and the right part of the glacier.
The Jungfraujoch railway station (3,450 m) gives a direct access to the upper Aletsch Glacier as well as the normal route to the Jungfrau. It can be reached only from Interlaken in the canton Berne. Glacier tours can be done with the help of the Konkordia Hut or the Hollandia Hut, eventually reaching other glaciers in the massif.
On the Riederfurka, at 2,065 metres between Riederalp and the glacier, is located the historic Villa Cassel, former summer residence of many numerous famous and influential guests from the worlds of politics and finance. The house is now one of the centers of the environmental organization Pro Natura, which hosts a permanent exhibition about the site.