In search of a new challenge, Swiss mountain climber Ueli Steck gets into peak condition to break the speed-climbing record for the three most notorious northward faces in the Alps: the Eiger, the Grandes Jorasses and the Matterhorn.

Annelie Pompe embarks on a mission to both scale the heights of Mount Everest and freedive to the lowest recorded depth of the ocean, an achievement that would make her the record-holder for a woman who has reached the greatest height and depth.

BASE jumper Karina Hollekim risks an extreme 600m jump from Hand of Fatima in the Malian desert.

South African kayaker and adventurer Steve Fisher plans one of the riskiest projects of his career: navigating the narrow canyons of the Zambezi river below the Victoria Falls during one of the most extreme high-water periods in history.

The Oceans Seven are the seven most treacherous ocean channels in the world to swim across. No human has ever done it, but Irish marathon swimmer Stephen Redmond has conquered six. Now he hopes Tsugaru Channel in Japan will be his grand finale.

In 2011, Thomas and Alexander Huber with Mario Walder were the first climbers to attempt a redpoint team free ascent of Mount Asgard on Baffin Island, Canada. After 28 pitches, the three climbers stood atop its South Tower.

On every new and full moon, an enormous tidal wave occurs along the lower Amazon. It's a tempting target for surfers despite the wave power, water hazards and isolation that make it dangerous, but a team of pro big-wave surfers accept the challenge.

Nearly 60 years to the day after the first ascent up Mount Everest, Russian mountaineer Valery Rozov attempts to fly off the north face of Mount Everest and achieve the world's highest BASE jump ever at 7,220m above sea level.

Survivalist Joe Vogel dares the crossing of the most unforgiving desert on earth: 240km across Bolivia's vast salt lake known as the Salar de Uyuni. After an aborted attempt with a partner a year ago, Vogel makes the perilous journey solo.

Sebastian Copeland and partner Eric McNair-Landry cross 2,300km of the Greenland ice sheet. Braving a week-long blizzard in a small tent, the duo set a world record for the longest distance travelled on skis and kites in 24 hours.

Australian hang-glider Jonny Durand sets out to perform loop-the-loop aerobatics on the leading edge of the so-called sky tsunami, Morning Glory, a rare, 2km-high tube-cloud phenomenon that clings precariously low to the ground.

Eighty metres of mystery lies between two giant cave systems deep beneath the New Zealand wilderness. If Troy Watson and Kieran McKay can connect the Nettlebed and Stormy Pot systems, the find will be the biggest cave in the southern hemisphere.

Ten skiers, filmmakers, writers, photographers, and sailors set off on a journey to ski the Antarctic Peninsula. Chris Davenport, Stian Hagen and Andrea Binning hike and ski new peaks in one of the world’s last, largely unexplored regions.

Ice climber, Will Gadd, pushes the boundaries of the sport by climbing the frozen 140m-high cave behind Helmcken Falls, BC, Canada. He faces freezing temperatures, exhaustion, and an ever-changing landscape.

The Inga Rapids of the Congo River are the holy grail of kayaking, with bigger and more dangerous waters than anywhere else on earth. Steve Fisher and his team set out be the first to run this 50-mile, churning behemoth of white water.

Attempting the first ascent on the face of Mount Roraima, located deep in the jungles of Guyana, is an insatiable draw for climbing legend Stefan Glowacz and his team. But a tragic accident changes the drive to conquer this massive, majestic, mesa.

Majlis al Jinn, a huge subterranean chamber in Oman, is big enough to house the Great Pyramid of Giza. Climbers Chris Sharma and Stefan Glowacz attempt an ascent from the bottom of the cave, up the massive arch, back to the light of the surface.

Rafa Ortiz and a group of kayakers who specialise in big waterfall drops attempt to run a section of the Mexican Rio Santo Domingo that is the steepest navigable whitewater on Earth. It's a feat that nearly killed Rafa just four years prior.

Zeb Walsh has dreamed of paddleboarding the channel between Australia and Tasmania since he was 15 years old. In his death-defying attempt, he enlists two friends to brave the choppy, shark-infested waters of the Bass Strait and make history.

Combining the fastest elements of both skiing and paragliding, speed riding is one of the most exciting winter sports in the world. Jon Devore and some of the most accomplished athletes in the sport want to tackle the 'unrideable' giants of Alaska.

The Bahamas are home to some of the world‘s most stunning and extensive underwater cave systems. Diving legend Brian Kakuk believes that two of the biggest systems there are actually one massive one and he is determined to prove it.

Two veteran paragliders, Will Gadd and Gavin McClurg, attempt to complete the first paragliding traverse of the Rocky Mountains, North America‘s most iconic and wildest region. The 1200km trek will be a world record flight if they make it.

Antarctica's Mount Erebus, the most southern active volcano, has one of only five permanent lava lakes in the world. British geologist Clive Oppenheimer sets out to measure the temperature of the volcano’s lava, but faces random eruptions as he does.

An adventure that's also part scientific exploration, a group of climbers attempt to descend into an active volcano to get as close as possible to the spitting lava lake. They brave poisonous gasses and 1,093°C (2,000°F) heat climbing into the earth.

Mitu Monteiro, a former world champion kite surfer, attempts to ride to the 12 volcanic islands of his homeland completely solo. It's a challenge he hopes will help unite the people of Cape Verde, but he's never tried anything like this.