Ultra-Trail du Mont-Blanc (UTMB)

UTMB is ultrarunning's toughest single-stage challenge, with elites covering 171 kilometers of Alpine terrain in under 21 hours. Elevation gain exceeds 10,000 meters, demanding more vertical than Comrades Marathon (#7) and Tokyo Marathon (#6) combined in a single loop. As the sport's World Cup, it attracts a deeper elite field than any other trail event, and its finish rate drops below 50% each year—a stark contrast to Tokyo Marathon's 98% finish rate. This brutal course cuts through France, Italy, and Switzerland, testing even seasoned ultrarunners with relentless grades that average a 12% incline.