On each Sunday between November and March, about a hundred people from all stages of life gather on New York’s Coney Island Boardwalk. They chat, they joke, and then they undress. At one o’clock sharp, somebody blows into a conch shell. This is the signal for the Coney Island Polar Bears to run down the beach and throw themselves into the Atlantic Ocean, no matter whether there is brisk sunshine, snow, a drizzle, or a blizzard. Some stay for a minute, others stay for longer. Some only dip, others swim. When the spectacle ends, perhaps half an hour later, the people’s skin is pink, but the spirits of the swimmers have risen high. High enough that they will be back in another week.