L'Ultra Marin is an annual trail running series around the Gulf of Morbihan in Brittany, held in late June or early July since 2005. The main race is a 175 km ultra starting and finishing in Vannes, with participants allotted 42 hours, including any stops. The event includes both amateurs and professionals, with entries capped at 1,000 for the main ultra and 10,000 overall to minimize impact on the coastal paths.
The long course circles the gulf entirely on coastal trails. An organized ferry crosses between Locmariaquer and Arzon before the finish at the port of Vannes. The series also features a 100 km race from Arzon, a 56 km trail from Sarzeau, the 34 km Ronde des Douaniers from Séné, a 29 km Nordic walk from Séné, and a four-person relay on the 175 km route. While the distances are substantial, the elevation gain is moderate for trail running, distinguishing it from mountain ultras.