The Marble Caves are outcrops of solid marble standing in General Carrera Lake, the deepest lake in South America, in the Aysén region of Chilean Patagonia. The stone is far older than the holes in it. It began as limestone on an ancient seabed and was recrystallised into marble long before any lake existed here. Glaciers gouged out the basin and pulled back about fifteen thousand years ago, and only then did water start dissolving the exposed rock. The caverns are roughly six thousand years of that work, and it has not stopped. The walls come banded in grey, white and soft pink: iron oxides make the pink and rust streaks, carbon the near-black ones and clean calcite the white, so a single wall can show all three within a metre.
Boats and kayaks go out from the village of Puerto Río Tranquilo. A kayak gets into the narrow slots between the outcrops that a motorboat is too wide to enter, and inside you float an arm's length from the marble while daylight bounces off the water and runs in ripples across the ceiling. That light is glacier-made. Meltwater carries rock flour ground so fine it never settles, and the suspended dust throws the lake's turquoise up onto the pale stone. Waves have also worn openings clean through the thinner walls, so from inside the caverns you look out through windows of marble at the water and the snow-streaked peaks behind it. How far in you get is decided by the lake. Summer meltwater lifts it to its yearly high and seals off the inner chambers that locals call the Chapel and the Cave; when the level drops in autumn or early spring, a hull can nose right under the arches into them. The free-standing islet out in the middle, the Cathedral, is reached at first light, because the wind here gets up by late morning and cancels boats without warning. The water you are floating on is still dissolving the wall an arm's length away.