The stories of mountaineers who have reached the summit of the world's tallest mountain, including a look at the dangers of the low oxygen levels at high altitudes. The programme examines the factors that allowed Edmund Hillary and Tenzing Norgay's 1953 expedition to succeed where so many had failed, and reveals how the Sherpas, who work as porters and guides for expeditions, have a physiology uniquely adapted to surviving at high altitudes.