Hallingdal is one of Norway's major valleys. It cuts through the bedrock for about 150 km from Lake Krøderen to Hardangervidda at Geilo. Hemsedal is a branch of the main valley. Road 50 runs through the Hol branch towards Flåm/Aurland at Sognefjord. The valley floor is gentle while the surrounding hills and mountains are steep and home to several ski resorts. The valley is also home to road 7 (a key east-west road) and Bergensbanen (the Bergen railway line).
In the barren mountains the reindeer is master, while the forests is home to a large number of elk/moose ("elg"). Some brown bears also thrive there, some are kept in a park (zoo) at Flå.
Hallingdal generally enjoys relatively dry continental climate (warm summers and cold winters). Winters can be bitterly cold in the interior. Nesbyen has the highest recorded temperatures in summer in Norway and usually among the warmest places in summer on average. Winters are also relatively cold. At Geilo temperatures are consistently below 0°C (frost) from December through March, most of November and April are also below 0°C during night. There is modest precipitation in Hallingdal. Wind can however be rough on the exposed mountain plateaus.