When Amundsen reached the South Pole in 1912 there was only one great challenge of polar exploration left - to cross the Antarctic from sea to sea.
Shackleton left England in September 1914 with this in mind but things quickly turned sour when his ship the Endurance was trapped in ice floes. This marked the beginning of an extraordinary story of survival.
Shackleton and 5 crew members set out in an open boat in treacherous seas at constant risk of capsizing. After 15 days they arrived on the wrong side of South Georgia and had to cross uncharted mountainous terrain to finally reach civilisation.
Shackleton promptly set out again to rescue the 22 men left behind. All survived.