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 team of heroes into the remote Cotahuasi Canyon - the deepest gorge on the planet - in search of the lost Incan city of Marpa.

It is make or break for Ben and the team as they face a punishing ascent to reach their campsite 4,000m up on the canyon rim. The equivalent to climbing Ben Nevis three times in searing 40-degree heat, it is a daunting prospect, so Paralympic swimmer Giles leads from the front. But as the team climbs ever higher, it is soon clear that charity worker Ann is close to exhaustion. Show less