Four teams, the Military, the Endurance team, the Alaskans, and the Lower 48, face forbidding peaks, deadly tidal waves, massive glaciers, bottomless crevasses, man-eating predators and treacherous whitewater. Each leg, teams have just 60 hours to make it from start to finish, surviving off the land with only the gear on their backs. No GPS. No phone. No mercy. This fight to the finish isnb2(Bt about money or a prize; it's about pushing the limits of human endurance.