Ben Fogle is on an epic South American adventure across the Andes from the Equator to the Tropic of Capricorn.

He is now in southern Peru on the third leg of his journey, leading a new team of heroes into the remote Cotahuasi Canyon, the deepest gorge on the planet, in search of the lost Incan city of Marpa.

The team makes a perilous 1500m descent following a steep animal track down the sheer rock strewn gorge. It's a punishing trek and Paralympic swimmer Giles is struggling with altitude sickness. Determined to make camp before nightfall, the team rafts the deadly rapids of the Cotahuasi River but when their boat runs aground, relief worker Philippa is forced to face her greatest fear. Show less