DULUTH, Minn. – I crossed the dunes at Park Point and took in the wide expanse of beach. The August heat was rising, the sky shone a brilliant blue, and a teenaged lifeguard in red trunks climbed the ladder to his chair, with not a swimmer in sight. I kicked off my sneakers and stepped into the surf.

For a few seconds, everything felt normal. Then I looked down and noticed, through the crystalline water, that my feet were losing what little color they had, as if the blood were fleeing up my legs. After 15 seconds, discomfort was turning into pain. My toes screamed. Finally, after 23 seconds, I couldn’t stand it anymore. I stepped out of Lake Superior and my numb feet radiated their gratitude.

My “swim” at Park Point was over. Yet my exploration of this strange isle – with miles of windswept beach that look more like the Outer Banks of North Carolina than the North Shore of Minnesota – had just begun.