Ultramarathons easily earn the spotlight for their grueling conditions and lengthy distances, but a few of the 26.2 races are beefing up the traditional event with tougher courses, meaning more variety for the endurance runner.
In many of these extreme races, qualifying is difficult and finishing percentages can be drastically lower than a conventional road race. Still, it's a test many have chosen to take. There are dozens of extreme races to choose from—here's a look at 10 of the toughest footraces in the world.