2. Hell's Peak

Dropped naked in the British wilderness, Luke and Katharine are exposed to dangerously low mountaintop temperatures, while Amie and Michael seek support from some cyclists.

3. Giant's Gully

Couple Sion and Gareth struggle without their gadgets while strangers Dylan and Pete are attacked by insects, in an epic race deep in the Scottish Highlands - completely naked.

4. Hunter's Fury

Ant and Kim go off-route in search of food, whilst Terry and Luke rally together when an injury unexpectedly hinders their progress. Two teams miles off the beaten path - without a thread of clothing!

5. Dark Pines

Dropped naked in the clouds on a freezing mountaintop, strangers Lilly and Luke race against couple Claire and Beau. Luke with life in the wilderness, and vegetarian Claire faces a moral impass.

6. Doom Valley

Mark and Kristian struggle to start a fire. Jenny and Darren's route down the mountain is made tougher by Jenny's fear of heights. And one team's map-reading sends them miles in the wrong direction.