2. The Badwater Ultramaraton
Around 70 competitors and their sled dogs enter “The Last Great Race on Earth” every year to take on the dangers of the Alaskan tundra. The 10-day trail takes them from jagged mountain passes down through frozen rivers and lakes, forcing them to confront wind-chill temperatures of -70˚C, blinding snowstorms and treacherous tracks. At least 109 dogs have succumbed to the grueling conditions since its advent in 1973. No humans have died, but there’s always a first time.