The World's Toughest Races?8 images

Hardrock 100 endurance run is held on a loop course on 4WD roads, dirt trails, and cross country in Southern Colorado's San Juan Range, USA.

The Everest Marathon is the world's highest marathon and starts at Gorak Shep at 5,212 m (17,100 ft), the site of the 1953 Everest Base Camp.

The Barkley Marathon takes place off trail and without any aid. Participants must use maps to find their way to books, hidden under rocks and in old stumps, from which they must tear a page. Credit is not given for a loop unless the...Plus

Ultra Trail du Mont Blanc, Alps, France. Non-stop 103 mile mountain marathon across three countries and 10 mountain passes.

The Patagonian Expedition Race takes place in the remote wilderness of Chilean Patagonia. It takes place on a different course each year, with competitors using a map and compass to navigate through previously unknown terrain.

Badwater Ultra, a 135-mile course starting at 279 feet below sea level in the Badwater Basin, in California's Death Valley, and ending at an elevation of 8360 feet at Whitney Portal. Very few people are capable of finishing this...Plus

Norseman xtreme triathlon in Norway begins with a 4m dive into a freezing cold fjord, before requiring competitors to swim 2.4 miles to shore. You will then cycle 112 miles across five mountain passes, before running a complete...Plus