A few summers ago I was on vacation with my children in Minnesota. It was early evening, and I needed a way to occupy them for a couple of hours in order to make it to the end of what felt like a very long day. I was tired, and my fuse was short. I had them put on their bathing suits, and we piled into the car, heading to what someone had recommended as a perfect swimming spot in one of the 10,000 lakes surrounding us. In the wilderness, my GPS was less than helpful. I turned down one gravelly dirt road after another...