The men pick their route: some take the higher land, some follow the river. Expert climber Willi Prittie leads Brent Sass and Tyler Johnson into the mountains. The bearing they're traveling reaches elevations over 4,000 feet. Veteran mountain man Marty Raney is leading his son Matt and survival expert Austin Manelick through the river valley. Brothers Dallas and Tyrell Seavey navigate along the ridgeline, crossing land with little cover. These born racers are resolute to be the first to arrive.

The men are divided into two groups, building competing rafts. Mountain man Marty Raney is taking charge, building a colossal raft weighing nearly 2 tons which he hopes will be sturdy enough in the rapids. After spending five hours on construction, the five-man crew get on their way, but hunger starts to take its toll. Dallas Seavey, his brother Tyrell and survival expert Austin Manelick are meticulously engineering a smaller raft that's speedy and maneuverable to tackle the turbulent Yukon.

Helicopters leave the eight explorers on a snow-capped summit. The men split into three groups and approach a 300-foot cliff, descend a ravine and traverse eight miles of the Triumvirate Glacier. Marty Raney, his son Matt and Brent Sass take a low route and are the first to cross. Willi Prittie and the Seavey brothers cross far from the icebergs, across 33-degree water. Austin and Tyler bypass the glacier, traveling along the ridgeline. They arrive last and Austin's showing signs of hypothermia.

The eight explorers are on the fourth leg of their expedition and are struggling to stay afloat on the Talachulitna River. With currents rushing at dangerous speeds, it's no easy feat to navigate the frigid waters. Expert climber Willi Prittie teams up with Iditarod champion Dallas Seavey and his brother Tyrell to find a much-needed food source. Meanwhile, mountain man Marty Raney and his son Matt enter the river further downstream hoping to minimize their time on the water.

The explorers brave the dangers of Alaska's "Bear Highway" only to find themselves stranded and fighting to survive Mother Nature's fury on the shores of Katmai Bay.

Facing the brink of collapse, the eight starving explorers set out with one mission: harvest as much food as possible from the barren landscape of Nunivak Island.

On day 32 of the expedition, the explorers traverse the Nizina River Valley, a vast expanse of land known for its lush wildlife, hungry grizzlies and homesteaders living hundreds of miles from civilization.

The explorers travel to Admiralty Island, home to the highest density of brown bears in North America, and it's not long before they receive a "grizzly" welcome.