1. The Vail Pass Half Marathon
Whist a half marathon is 13.1 miles worth of child’s play compared with some of endurance events on this list, stick that run 10,662 feet above sea level where there is roughly 21 per cent less oxygen and it quickly becomes a throat burning battle of the fittest.
One aspect of the annual Teva Mountain Games, hosted by the outdoor footwear company, a further 2,900 feet of elevation to tackle during the run, oxygen starved muscles become lead weights to drag you up the side of a snowy mountain. Oh, and did we mention the possibility of altitude sickness, nose bleeds and lung busting shortness of breath before you even cross the start line?