Bislett 24 Hour Indoor Challenge

Bislett 24 Hour Indoor is a 24-hour ultramarathon held indoors in Oslo, Norway. Rather than a point-to-point race, participants spend a full day covering as much distance as possible under controlled indoor conditions. The race is sanctioned by the International Association of Ultrarunners, the global body for ultrarunning under the patronage of World Athletics. Its IAU listing places it on the formal ultrarunning calendar, distinguishing it from informal endurance challenges.