Río Aguas Calientes

This guide to the Río Aguas Calientes follows the confusion that gave the river, and the town beside it, their name: a barefoot traveler wading in and finding the water warm, then hot, with no pipe or fire in sight. It traces that heat back to a vent about a kilometer upstream, where groundwater meets warmth rising from deep in the Andes and picks up sulfur, calcium and iron on its way to the surface. You'll hear what that chemistry does to the water's color and smell near the source. Follow the current either direction and you're tracing the same journey the heat makes into town.