The Sondu Miriu river drops off the western edge of the Gusii Highlands in a steep gorge that has been partly tamed by a hydroelectric scheme but still offers some of the best river scenery in this part of Kenya. The dam, completed in 2008, supplies a sizeable share of western Kenya's electricity.
You can drive to a viewpoint above the gorge in a couple of hours from Kisii, and from there walk down rough paths to the river. The walk is steep but rewarding — there are pools, falls and, in the steeper sections, monkeys and many birds. Take a guide from one of the villages above the gorge.