It is never a good idea to pause between a 194-degree sauna and the mind-bending frigidity of Lake Superior in February. As sweat cools on skin, the rational mind kicks in. Why submit the body to such unrelenting shock, it asks. Yet here I am, on a cobblestone beach in Grand Marais, Minn., with precious heat steaming off my head, pausing to contemplate the wave-sculpted ice that appears to be growing toward the sky like stalagmites.