Survivalist Bear Grylls is partnered with actor and director Ben Stiller for a 48-hour, action-filled trek, pushing them to the limit both physically and mentally. Bear is keen to find out whether Ben, who has braved his share of stunts in films such as Zoolander and Tropic Thunder, can handle a trip into the wilds of Scotland. The expedition begins on the shores of Loch Harport on the Isle of Skye and as it progresses, the two must rope themselves together to scramble up and over a ragged set of rock cliffs, seek shelter, descend into the darkness of a vast cave to find a pool of fresh water, use an ascender - a combination of rope and hardware - to pull themselves straight up a sheer wall, and leap 40ft off a cliff into the North Atlantic, before finally swimming to a seaplane to climb on board

• Bear Grylls