Bear Grylls takes comedy writer and actress Miranda Hart on a once-in-a-lifetime expedition to the spectacular Swiss Alps.

Bear challenges novice Miranda to go far beyond her comfort zone with a series of exhilarating adventures during an intense two-day expedition.

Miranda traverses a glacier, crosses crevasses roped to Bear, tackles deep snow in snow shoes and completes a huge boulder scramble. She also faces her greatest fears when she flies in a helicopter and abseils down a waterfall.

Bear Grylls helps Jonathan Ross to discover his inner Tarzan on a once-in-a-lifetime expedition to the magnificent rainforests on the volcanic island of La Palma, one of the least-known of the Canaries.

Bear challenges novice Jonathan with a series of exhilarating adventures during an intense two-day trip, including trekking through dense jungle with machetes, SAS-style fast-roping from a helicopter, a walk down an active volcano and sleeping in a cave in a steep cliff face.

Bear and Jonathan have to fend for themselves, including preparing wild animals for food.

Bear Grylls pushes Stephen Fry to his limits with a series of incredible challenges on a once-in-a-lifetime expedition to one of the most spectacular mountain ranges in Europe.

Over the course of two days, high in the Italian Dolomites, Stephen travels on the skids of a helicopter, climbs down a raging 500-foot waterfall, sleeps in a First World War trench and abseils down a towering cliff face.

Stephen and Bear face treacherous conditions as a freak summer snow storm hits the mountains, and Stephen must face up to some of his deepest fears.

He also talks frankly about some of the other challenges he has faced over the years, including prison, his body image, bipolar disorder and a near fatal suicide attempt.

'My hope is that I will be a little bit more proud of myself at the end of it and at least feel that I've accomplished something.' says Stephen.

Will Bear break one of our national treasures? Or can Stephen overcome everything thrown at him and face his demons head on?

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