To portray the hero of the Thai cave rescue in the new film Thirteen Lives, the Hollywood star had to go deep—literally. Mortensen plays the part of Rick Stanton, the legendary British cave diver who helped lead the rescue of 12 boys and their soccer coach from the far reaches of a flooded cavern in northern Thailand. The actor’s preparation included months of conversations with Stanton and a harrowing cave-diving adventure of his own. In this episode, producer Paddy O’Connell talks with both men about what it takes to endure the mental and physical challenges of swimming through dark, tight spaces, where just one mistake can kill you.