Gudbrandsdalen is a valley and traditional district in the Norwegian county of Oppland. The valley is oriented in a north-westerly direction from Lillehammer and the lake of Mjøsa, extending 230 kilometers (140 mi) toward Romsdalen. The river of Gudbrandsdalslågen (Lågen) flows through the valley, starting from Lesjaskogsvatnet and ending at Mjøsa. The Otta river flowing through Otta valley is a major tributary to Lågen.