efe-epaSalzburg, Austria

The world’s longest endurance race is taking place in the shadow of the Austrian Alps in a park in Salzburg, where competitors have to run 5,000 kilometers (3,106 miles) in 52 days — more than two marathons a day.

Five athletes have been taking up this challenge, known as Self-Transcendence 3100 Mile Race, which is the longest certified foot race in the world. EFE-EPA