Sahara Desert. They find themselves at the mercy of a former Foreign Legion instructor. Taking them into the Sahara, he subjects them to a series of gruelling challenges, including being buried alive, a 10-kilometre camel race, and an exhausting run over the sand dunes while wearing stifling gas masks.

US Navy SEALs. They travel to Virginia to carry out "simulated" Navy SEAL training with some former US Navy SEALs, whose beach-based challenges from long beach runs to "surf torture" leave them physically and emotionally drained. After the first day Carla suffers from dehydration and exhaustion, but must face her fear of water in a drownproofing challenge where the volunteers repeatedly sink in a pool with their ankles and wrists bound.

Everglades. They will be sharing the territory with two million alligators and 60 species of venomous snake, and perhaps most formidable of all, their Native American guide. “My name is not important to you,” he sneers. “But you will call me Teacher.” They have to cut open an alligator and remove its entrails with their bare hands. They canoe across alligator infested waters and wrestle alligators, and play a game of lacrosse.