The heat—I’ll always remember the heat. Total, all around me, consuming, baking my body like a bit of steak in a sous vide. Climbing into a long, shallow hole dug by two industrious women, they quickly began covering me up, shovel by shovel, until almost everything, arms, legs, even neck, was underneath. With only my face and the top of my head emerging from the black, volcanic soil, I quickly began to sweat, the perspiration trickling down my face and disappearing into the ancient dirt. They told me it was good for me, great for the skin—a restorative process. Stay submerged for 15 minutes, minimum. But after 10, the heat still rising, I was ready, shaking off my sand bath and headed to rinse off in the onsen (the hot spring). I was on Kyushu, the southernmost of Japan’s main islands, and a land of hot springs, geysers, and bubbling …