'Walking the Nile' explorer Levison Wood takes on a new challenge in this 5-part series: to walk the length of the world's highest mountain range from Afghanistan in the west to Bhutan in the East. His four-month journey of some 4 million steps sees him trekking 1,700 gruelling miles across the roof of the world, teaming up with local guides and meeting monks, soldiers and nomadic tribes, as he passes through some of the most remote, beautiful, and perilous regions on earth - places few outsiders ever get to see.