Forget relaxing on holiday; more travellers opting for physically punishing adventures in some of the world’s toughest places. For Sara Storey, the World's Highest Marathon offered a chance to do something nobody had attempted before. "I've done quite a few ultramarathons and multi-day races, some of them quite tough, but I'd never experienced an event where so much effort was required even to get to the start," she said. She was one of 16 runners who signed up for the World's Highest Marathon