Le Trail du Tertre Gris is a trail-running series based in Pancé, a small commune in Ille-et-Vilaine about 20 minutes south of Rennes on the Rennes-Nantes road. It is usually run in early July, with distances from 5 km and 12.5 km up to 26 km and the long MaraTrail, so the same event can suit first-time trail runners and people looking for a harder day out. The shorter courses avoid major difficulty, while the long race goes well beyond marathon distance and climbs more than 900 metres, with some listings giving it around 48 km and 1,100 metres of ascent.
The routes use the valleys of the Semnon and the Vilaine, passing local sites such as the Moulin du Boel, La Courbe at Bourg-des-Comptes, the levee and Croix des Jeunes at Plechatel, and the Tertre Gris site that gives the race its name. The organising team has been working on the event for 15 years, with a clear idea of progressive courses: easy access for runners discovering nature racing, then more technical ground for the longer distances. It also puts effort into lower-waste logistics, including less plastic, waste sorting at aid stations, and course markings reused from one edition to the next.