Karelian Seikkailu-urheilijat ry, known as Karsu, is an outdoor sports community based in Joensuu with around 80 members. The association brings together people interested in adventure sports, multisport and trail running, and offers members courses, group training sessions, competitions and shared events. Its members take part in adventure races across Finland, as well as trail-running events, the Jukola relay and other activities related to sport and exercise.

Karsu’s programme is largely organised and delivered by volunteers. Members help create events for the wider sporting community, including Ursak adventure races, the Vaarojen Maraton trail-running event in the Koli area and Wiima, a winter adventure event. Vaarojen Maraton is known for its challenging trails and distinctive setting in and around Koli National Park. The association also shares articles, videos and event information, and provides members with access to equipment reservations. Through its activities, Karsu supports participation, shared experiences and an active outdoor lifestyle for both its members and event participants.