What do you get when you mix mountains, deserts and the most toned calves this side of, er, anywhere? These awesome running trails, that's what.
From alpine climbs in the shadow of the Matterhorn to boulder hops at the deadly sandstone jaws of the Grand Canyon – here are the world's most awesome endurance challenges.
Photographer, podcaster and running aficionado Ian Corless's new book Running Beyond: Ultra, Trail and Skyrunning Races explores the planet's most outrageous ascents and epic alpine climbs for the delight of joggers and sofa dwellers around the world.
Running Beyond by Ian Corless is published by Aurum Press for £25, amazon.co.uk