Courses nature de la Baie d'Isigny begins and ends at the town hall in Isigny-sur-Mer, located on the Normandy coast in Calvados. Held in late February, it offers runners two short trail routes: 10.5 km on Les Sentiers du Caramel or 17 km on Les "dix-huitres" Kilomètres du Caïeu. The Association des Marathoniens d'Isigny sur Mer organizes the event, which includes chip timing and a maximum of 700 participants.
The courses are approximately 90% trail, winding through the port of Isigny, seaside dikes, polders, and the hedged bocage paths of Normandy. The longer race has a strict cutoff: participants reaching 12 km after 1 hour and 25 minutes will not be classified. The local character is evident in the prizes, which consist solely of regional products like oysters, caramels, and Camemberts, reflecting Isigny-sur-Mer's strong association with butter and cheese production.