Sarnen is the capital of the canton of Obwalden situated on the shores of Lake Sarnen (Sarner See), Switzerland. It has a population of just under 10,000 and is surrounded by countryside and mountains. Sarnen is located 20 km south of Lucerne.

Stone Age and Bronze Age finds show that the Sarnen valley was inhabited from the earliest times. Over the years Sarnen developed into an important trading center.

Sarnen is situated at an altitude of 473 m (1,552 ft) on the shore of the Lake Sarner (Sarner See). Lake Sarner covers approximately an area of 7.5 km² (2.9 sq mi). The town is surrounded by mountain chains and a protected bog can be found nearby. The most well-known mountain close to Sarnen is Mount Pilatus with an elevation of 2,132 m (6,995 ft).

Sarnen has an area, as of 2006^[update], of 73.1 square kilometers (28.2 sq mi). Of this area, 40% is used for agricultural purposes, while 50.9% is forested. Of the rest of the land, 5.2% is settled (buildings or roads) and the remainder (4%) is non-productive (rivers, glaciers or mountains).