Tough Guy or Chicken

To start their epic journey they travel high into the Andes where they must become chagras - the weathered, hard-as-nails cowboys of Ecuador. They do battle with the local, deadly fighting bulls, many of which end up in bullrings across South America. The Brits arrive at the busiest and most dangerous time of year, the rodeo. This is when thousands of fighting bulls are rounded up in the mountainous foothills to be counted, branded and vaccinated. They have six days to prove themselves and, if they are good enough, to take part as one of the locals. Top chagra Gerardo has the task of training them. To become chagras the boys must learn to ride like chagras and to use a lasso, practising skills to avoid being impaled by a charging bull. It's a tough crash course. How will vegetarian Ben cope where slaughter and steaks are a part of everyday life? What about new age traveller Reuben, who isn't used to following orders? Can any of them deal with the threat of altitude sickness at 4,000m, or the heavy drinking of the local chagras?

Continuing their epic journey they travel to the Siberian arctic to become Evenki reindeer herders, a people who have survived in one of the most hostile locations for thousands of years. This is about learning to deal with extreme cold without home comforts. The Brits arrive in a world that is lifted straight from the ice age, but for locals it is what they call spring. It is one of the busiest times of year, when reindeer herds need to be corralled and moved to new pastures. The boys have just six days to prove themselves to their trainer for the week, Evenki herder Nikolai Mikhailovich. To become Evenki they must learn to control a reindeer sledge, the only reliable form of transport in a place where motor vehicles crack and fuel freezes. If they satisfy Nikolai they will travel out to the herd, making camp in bone-snapping temperatures and attempting to fish through a metre of ice. If they come through it all they face the ultimate challenge of staying out all night, guarding Nikolai's herd from local wolves. After his experience in Ecuador will veggie Ben cope when there is only meat on the menu again? Has Easton recovered from his altitude sickness and his injured pride, and can Reuben learn not to ignore everything his trainer says?

The adventurers head into the jungle of Mexico's Yucatan peninsula and become cave-divers in a vast network of largely uncharted, pitch-black, underwater tunnels. The Yucatan was once a centre of the Mayan empire, and the openings to this watery underworld were sacred. Deep in one of the caverns, close to an ancient temple, a Mayan graveyard contains suspected victims of human sacrifice. The boys have just six days to prove themselves to their trainer for the week, top cave-diver Sam Meacham. If they do, they will assist him in an archaeological expedition to explore this mysterious site. For cave-divers death is an ever-present threat and the boys will have to show they can overcome extreme claustrophobia, intense scuba diving drills and an ability to never panic. After failures in Ecuador and Siberia, Ben and Easton are desperate to complete a challenge, but it looks like the smart money is on top watersports athlete Ross for this one.

The adventurers join boys of the Jaminawa tribe in the Brazilian Amazon and endure six days of a jungle initiation to become men. To succeed they must follow the rules of Jaminawa shaman Carlito, who has taught generations of boys the secrets of the jungle the hard way. The modern world is fast approaching the edge of Jaminawa territory, and Carlito is intent on keeping ancient traditions alive for the next generation. He is taking ten local village boys into the jungle to learn its secrets and commune with its spirits. For the first time, Carlito has agreed to take a group of outsiders. If the Brits are to emerge from the jungle as Jaminawa men they will have to do everything Carlito demands of them. It means taking strong hallucinogenic brews to enter the spirit world, involves hunting for crocodile and sacrificing a snake to obtain its secrets, and finally going through a trial-by-pain to atone for the snake's death. So far Ben and Easton have failed every task and this time they simply have to man-up. But since Nick conned his way through to the end of their previous challenge, the group of adventurers haven't exactly been best of friends. How will they cope when the pressure really builds up?

After two months on the road, they have arrived in blistering heat of the Namibian bush for their fifth challenge - to join the Ju-Wasi tribe of San Bushmen on a traditional hunt in an extremely inhospitable environment. The hunter-gatherer way of life practiced by the Bushmen goes back to the dawn of mankind, and they are supremely skilled in surviving in a place that has little food, virtually no water and arid, baking heat. Top hunter Duee has taken on the task of turning the five Brits into expert trackers and hunters in just six days - if they survive that long. They must learn to take food wherever they can find it, seek out muddy water in any crevice and make fire to ward off predators. Easton might be feeling pretty good after being named Carlito's top tribesman in the Amazon, but how will he deal with the heat and will he still be at Nick's throat after spats in Mexico and Brazil? Can veggie Ben really hack it as a hunter?

After the pain of the Amazonian jungle and the arid heat of the Namibian bush, they have come to paradise - the Bahamas. Unfortunately for them their challenge lies underwater, in the shape of sharks. Top shark expert Jeremiah Sullivan has taken on the task of turning the five rookies into shark wranglers in just six days. Jeremiah has been diving with sharks for 35 years, was the first man to be photographed holding the dorsal fin of a Great White, and as a day job he tests chainmail shark suits by getting bitten. To impress Jeremiah the boys have their work cut out. They must prove they can swim strongly enough to deal with the attentions of a two-metre reef shark; show they can handle the mental pressure of a shark feeding frenzy; and finally handle sharks directly, attempting to put one of these deadly creatures into a hypnotic state where it can be cradled like a baby. Climber Reuben is not sure he is prepared to risk losing a limb, while Easton's form as a swimmer is pretty weak. Even top watersports athlete Ross has a tendency to get seasick when the water is not in a swimming pool.

The lads' penultimate challenge is going to be one of the most deadly, as they have come to Bangladesh to learn to catch venomous snakes. Master snake king Shoporaj Dholu has just six days to train them up and keep them alive. Dholu comes from generations of snake kings. He is a Bedey gypsy, a caste known for its snake catchers, snake charmers and snake medicine. The Brits arrive in the Bedey village of Rahmatpur at just the right time - Dholu is planning the first snake hunt of the season, for deadly cobras, and if they are good enough he has agreed that the outsiders can come along. First, they have to prove they can catch rats and lizards, that they can handle milk snakes without getting bitten and that they can keep their head when confronted by a deadly cobra, while surviving 45 degree heat in 100 per cent humidity. Reuben looks to be in pole position because he actually loves snakes, but Nick is still determined to retain his incredible record of passing every challenge so far.

They have reached Japan for the last of their challenges. They have just six days to become Buddhist Yamabushi monks and take part in one of the toughest pilgrimages on the planet to the summit of a sacred mountain, under the watchful eye of Miyagi-San, their Master. The Yamabushi are a centuries-old sect that seeks enlightenment by experiencing nature at its most raw and the Brits have arrived just in time for the Okugake - an extreme pilgrimage to the top of a treacherous mountain ridge that is at the heart of the Yamabushi's beliefs. It involves four days of climbing, interspersed with physical and spiritual trials including the Nishino Nozoki - which involves being hung over a precipice while answering questions about your beliefs. Over the centuries many monks have been injured and even killed on the pilgrimage. Before the lads can start the quest they must learn how to live the ascetic life of the monks through meditation and prayer, and prove their mettle by chanting ancient mantras under an icy mountain waterfall. For Nick, it is his chance to complete every single challenge of the journey, but Ben is still waiting for that one handshake of success. And for everyone, the long, silent journey gives a chance to reflect on how their epic four-month challenge to take on the natural world has changed them as people.