Trail'oween - Les Clayes-sous-Bois 2026

Trail'Oween is a forest trail event held in Les Clayes-sous-Bois, located in the Yvelines region west of Paris. It takes place around the Halloween season, with recent editions scheduled for late October or early November. The event features two running distances: 10 km and 20 km. Additionally, a 10 km Nordic walk is offered, making the day accessible to more than just runners. The 10 km distance is more popular, having previously attracted over 300 participants, while the 20 km has drawn more than 100. Both trail races utilize single-loop courses entirely within the forest. The 10 km route includes a moderate amount of elevation gain, with recorded ascents ranging from approximately 175 to 240 meters. The 20 km course is more challenging in terms of hills, with sources indicating ascents between about 350 and 500 meters. The event contributes to Imagine for Margo, a French association dedicated to combating childhood cancer, providing the race with a distinct local charity mission that complements its autumn forest running theme.