UTMB isn’t just long—it’s relentlessly mountainous, unpredictable, and logistically complex. Here are 12 reasons the Ultra-Trail du Mont-Blanc is considered one of the toughest trail ultramarathons in the world.

1. Massive distance and vertical gain UTMB covers roughly 171 km (106 mi) with about 10,000 m (32,800 ft) of climbing around the Mont Blanc massif—an ultra-long route with continual ascents and descents that sap the legs and lungs (official race page: https://montblanc.utmb.world/races/utmb).