Tretten is a village in Øyer Municipality in Innlandet county, Norway. The village is located on the Losna lake, which is part of the Gudbrandsdalslågen river. Tretten is located in the Gudbrandsdal valley, along the Gudbrandsdalslågen river in the southern part of the municipality. It is located along the European route E6 highway, about 25 kilometres (16 mi) north of the town of Lillehammer. The municipal center of Tingberg lies about 5 kilometres (3.1 mi) to the southeast of Tretten.