Grylls parachutes into a Costa Rican rainforest in the Osa Peninsula, with only his knife and a canteen. He's careful about the water he drinks, but gets violently ill anyway. He climbs down a waterfall using a vine, and floats down a river to the ocean on a raft he crafts out of balsawood to demonstrate how someone lost in the jungle can make it to civilization. He encounters snakes, mosquitoes and dangerous river currents.ve swamps.