Long before Alcatraz, there was Devil's Island - the most notorious and vicious prison complex ever constructed. Over a century of operation, 70,000 men were incarcerated there. Built in the tropics of French Guiana, it was called the perfect prison - penned in by the jungle on one side and the sea on the other. Escape was said to be impossible. But was it? Olly explores the horrors of prison life and tests first-hand whether tales of great escapes could be true.