Six Thousand Years of Water Sanding a Wall

Lago General Carrera is the second-largest lake in South America and the wind can turn it into something with actual surf, so the boats go early or not at all.

We went at eight. The Capillas de Mármol are a headland of calcium carbonate that the lake has spent six thousand years sanding into colonnades and vaults, and the extraordinary part isn't the shape — it's that the water is clear enough to act as a light source. Blue comes up through it into the caves and moves on the ceiling.

Our boatman had done this run for eleven years and still cut the engine in the big chamber so we could hear it. Good man.