La Sancylienne is a mountain running weekend held in Chambon-sur-Lac, France, within the Puy-de-Dôme's Massif du Sancy. Taking place in early autumn, it now features two separate races: the Friday evening Verticale de Chambon des Neiges and the Saturday Ronde de Chaudefour. The vertical race is a short, direct 4.4 km with approximately 630 m of ascent, beginning together from Sancy Resort and run in semi-darkness. The Saturday race is the longer mountain challenge, covering around 16.5 km with about 1,050 m of elevation gain.
The location is the high, cold Auvergne landscape surrounding Chambon-sur-Lac, with lakes, ponds, ridges, and the Sancy crests. Previous versions followed a course of about 15 km from Chambon-sur-Lac to a finish at 1,400 m on the Col de la Croix-Morand, including one aid station and a four-hour time limit. The name Ronde de Chaudefour connects to the race's origins, and the event has over thirty years of local mountain running history. It attracts solo runners seeking steep, concentrated racing over extended ultras, with recent editions seeing around 300 participants.