For most runners, a marathon is the ultimate test of endurance, but for a select few, the standard 26 miles (42 km) simply isn’t enough. Around the world, extreme races push athletes into some of the harshest environments imaginable, from frozen oceans and scorching deserts to dense jungles and high-altitude mountain passes. Some also have bizarre extra elements thrown in, like racing against a horse or solving puzzles along the way.
So, from battling subzero winds to navigating the unmapped wilderness, click on to discover the craziest races on Earth.