Comedian Sue Perkins and adventurer Charley Boorman travel across Alaska to the notorious Dalton Highway - a dirt track built in the 1970s as a supply road to support the Trans-Alaska oil pipeline. Highway maintenance is a full time job here with avalanche units operating throughout the year. As Arctic conditions close in on them, the pair have to rely on the help of hardcore truckers for whom the highway is home. The rules of the road are: keep the CB radio switched on, don't exceed 50mph, and when an 18-wheel truck comes thundering down the rollercoaster of a road towards you, get out of the way!

Comedians Rhod Gilbert and Greg Davies attempt to drive through the mountainous, landlocked nation of Nepal.

Ben Fogle and Hugh Dennis travel from the Peruvian Andes to the depths of the Amazon, in search of the lost city of Constitucion.

Ed Byrne and Andy Parsons brave temperatures as low as 50 below to drive across Siberia's infamous Road of Bones.

Sue Perkins and Liza Tarbuck drive the legendary Ho Chi Minh Trail, a network of dangerous roads hacked through mountains and jungles of Laos and Vietnam.

Hugh Dennis and David Baddiel drive Ethiopia's bone shaking roads to reach Askum, home of the Ark of the Covenant.

During the tail end of the rainy season, Angus Deayton and Mariella Frostrup drive up Madagascar's eastern coast.

Hugh Bonneville and Jessica Hynes take a terrifying road trip through the former Russian state of Georgia.

Funny men Phill Jupitus and Marcus Brigstocke head to Bolivia for a high-altitude road trip that promises adrenalin, hilarity and drop-dead beautiful scenery.

Already good friends, the terrified duo first have to survive Bolivia's infamous Road of Death only to find themselves deep in notorious bandit country. Disorientation takes them by surprise as they have to navigate the stunning Salar de Uyuni, a salt lake so vast that Buzz Aldrin could see it from space.

Their goal is to reach the ancient mountain city of Potosi whose silver once financed the great Spanish empire but at almost 5000 meters above sea level this proves to be a heart stopping finale.