Conclusion. An adventure race in Costa Rica is featured.

Simon and Turbo train with expert bike racers and locals in the Alps before taking on the terrifying descents and harrowing switchbacks of the hardest mountain bike marathon in Europe: the 137-mile Salzkammergut race in Austria.

Adventure races take place in Costa Rica.

The 100 mile Yukon Arctic Ultra is possibly the coldest and toughest in the world. Racers battle the elements on skis and bikes, risking frostbite and navigation issues.

100km single-day race in some the most scenic areas of northern Mongolia. Our friends from last year’s Kenya return to compete with Simon and Turbo. The race itself is one of a kind and incredibly challenging. Epic in scope and the biggest, longest ultra we have tackled to date.

Simon and Turbo train with local experts and some of the UK’s top mountain runners before taking on the historic Ramsay Round in Scotland, a 56-mile race in which they attempt to summit 24 of the country’s highest peaks. In less than 24 hours. With no sleep and no support.

Hoping to redeem themselves after a disappointing upset in Hawaii, Turbo and Simon take on a five-day, eleven-city stand-up paddleboarding race through the picture-perfect canals of northern Holland. But redemption comes at a price: sweat and pain.

At the Great River Amazon Raft Race, Simon and Turbo pair with an inexperienced married couple to race 112 miles down a remote section of the mighty Amazon River. In 3 days. On a raft they built themselves. If they want to finish in one of the top spots, there’s a lot to learn, and quickly.

The guys attempt a 353-mile bike race through the California deserts.

In the Copper Canyons of northern Mexico is a remote and wild terrain where the CB Ultra race is held. This 75km race was featured in the book 'Born to Run' and is considered to be very special among ultra runners.

Simon and Turbo’s season kicks off with the intense “Fire and Ice Ultra” – a 250km, seven-day stage race – camping and running through the volcanic ruggedness of the Icelandic Highlands. Much to everyone’s surprise, winter comes early, and all runners battle the plummeting temperatures as a large snowstorm closes in.

The “Fire and Ice Ultra” foot race continues its way out of the Icelandic Highlands, north through ever-changing seasons towards the 250km finish line. But the cold and snow continue to be a risk factor for Simon, Turbo, and the rest of the competitors – and everyone has to stick together to overcome the challenges and safely complete the race.

The “Molokai 2 Oahu Paddleboard World Championships” is considered one of the toughest and most elite paddling races on earth. Simon and Turbo have four days in Hawaii to train before competing against the world’s best – and stand-up paddling their way over 10-foot open ocean swells to cross the 32-mile Channel of Bones.

The “Amazing Maasai Ultra” race pits a small field of international competitors against local Kenyans – considered some of the fastest runners on the planet – amid the heat and wilderness of the Laikipia Highlands. Simon is running this race without Turbo – he’s living in a small hut and learning all he can from the local Maasai Warriors – before pushing his physical and emotional extremes to complete the 75km single-day run.

The two-day, 82km “Hansa Fish River Marathon” paddle race on a river in rural South Africa boasts nearly two thousand kayakers rowing down man-made weirs and waterfalls, on class 3+ rapids. Simon and Turbo find themselves in way over their head, and fearing for their safety, have to decide between pulling from the race or finding a way to persevere and reach the finish line intact.

Taking their love of climbing, canyoneering and mountain biking to the extreme, Simon and Turbo head to Hurricane, Utah, to compete in the annual “Six Hours of Frog Hollow” bike race. The 12.8-mile looping course winds perilously through gaping canyons, alongside sheer cliff drops and over large boulders – presenting huge challenges for both guys, and a near catastrophic accident for Turbo.

There are few events in the ultra-racing community that hold as much prestige as the Four Deserts “Sahara Race” – a 250km foot race in Egypt over five days, through searing heat and sand, where day-time temperatures reach well into the 40’s. Simon is determined to place in the top rankings among the world's best, while Turbo battles ailments and near-exhaustion to hang onto his third-place position

The 250km “Sahara Race” continues across the Faiyum region of the Egyptian Sahara Desert, and as the days press on, all the racers become more worn down by the heat and long miles they are putting in. Turbo is forced into a major decision, while Simon pushes himself to the point of near-collapse, chasing down competitors and working his way up the ranks.

The “Ancient Khmer Path” is the first of its kind in Cambodia – leading runners 230km over six days through flooded jungles, ancient temples and rural villages in scorching heat and humidity. All the racers push themselves to their extremes – and when a good friend of Simon and Turbo suffers a life-threatening condition, they must find the courage to keep moving on and complete the race.

There is no global triathlon brand as renowned as the Ironman, and Simon and Turbo are heading to Phuket, Thailand to compete in a grueling 1.9km swim, 90.1km bike and 21.1km run. Falling ill with a stomach bug, Turbo fights to gain back his strength, while Simon prepares for the grand finale of their race season with the hope both friends can cross the finish line and end their race season on a high note

A 75 kilometer race through Mexico's Copper Canyons.

The "Burning Man" of the mountain biking world, this race attracts some of America's most eccentric mix, as competitors pedal a 24-hour loop course through the wild and dangerous cacti forest of the Sonoran Desert. The squad experiences equipment breakdowns, a race-stopping emergency, night time exhaustion and the fight to work their way onto the podium.

Set north of the Arctic Circle, this three-day cross-country ski race is considered one of the most challenging of its kind due to unpredictable weather conditions. The harrowing first day is full of learning curves, a white-out on day two challenges all the and a looming storm on the final day turns the entire race upside down.

The athletes head to the Atacama Desert, the driest place on Earth for a 100-mile foot race that could be the mental and physical breaking point of the race season. With the sun beating down on their bodies, it will take the pure determination of their minds to reach the finish line.

The Adventure Xstream Moab race in Utah is a riveting one-day, 60+ mile adventure competition. The race marks the first time Simon, Turbo, Rory and Hunter compete as a four-person team. Pushing the squad physically and emotionally against one another, they battle a crippling six-mile canyon climb, steep rope descents and a costly navigation blunder in their quest to make the podium.