The Trail du Bois de Trémelin is a forest trail race held in Inzinzac-Lochrist, Morbihan, Brittany, with recent editions taking place in late winter or around mid-March. It provides two route options: an 8.5 km run for a brief, intense effort, and a 16.5 km run for those seeking a more extended trail challenge. The race begins and ends at the Gymnase de Lochrist, and it is the second event in the Challenge Bro an Oriant.
The course crosses the Bois de Trémelin, meaning the race has mud, trees, and the conditions left by the Breton weather. One edition cautioned participants that sections of the forest were flooded, with two areas featuring water up to calf depth, even advising participants to bring extra clothing or a swimsuit. Each distance includes a refreshment station, parking is located approximately 1 km from the gymnasium, and a supervised cloakroom is available. The race has reached at least its ninth edition, attracting close to 800 participants across both distances.