The river rises near Tibet and is joined by the Bhoti Kosi just downstream from Barbesi. Most raft trips start at Dolaghat. The Sun Kosi flows eastwards in Nepal through the great valley between the Mahabharat Lekh range and the Himalayas.

A nice thing about Sun Kosi is that the general standard of the river gets progressively harder as you descend it so there is time to practice your skills on easy water before the more interesting, bigger and continuous rapids lower down the river.