Captain Louis Rudd knows what it's like to truly tough it out. He joined the Royal Marines at age 16, spent 25 years in the SAS and served in Northern Ireland, The Balkans, Iraq and Afghanistan. From a young age he was fascinated by tales from the ice and the expeditions of polar explorers like Robert Scott and Sir Ranulph Fiennes. It led him down to Antarctica several times, and on his most recent trip he undertook a 56-day, 1400km journey across the continent, becoming the second person and first Briton to do so. He's documented his gruelling journey in an appropriately named book: 'Endurance'.