Watch the famous Hemsworth siblings swim in freezing Arctic waters in EW’s exclusive clip from the National Geographic docuseries.

Hemsworth previously told EW he gained an understanding and appreciation “for how incredible the human body and mind is, and what potential we all have” thanks to the series. “It was one extreme after another — a series of scientific experiments where I was the guinea pig,” the actor said. “I was just in awe of the individuals I was working with who did this day to day.”

“There’s this very normal human fear of death that has kind of become a big point of conversation in culture right now,” Aronofsky added. “Mostly because the boomers are getting really old, and suddenly a lot of resources are going into the science of longevity. All the biggest tech companies have all these departments and wings that are looking into it.”