The Marble Caves are outcrops of solid marble on the shore of General Carrera Lake, the deepest lake in South America, in the Aysén region of Chilean Patagonia, hollowed by waves into caverns and arches that are paddled into by kayak and lit from below by turquoise water in every shade of blue. The marble began as limestone on an ancient seabed, recrystallised by heat and pressure long before any lake formed, and the caves are young, cut by six thousand years of waves; the stone is streaked and swirled in grey, white and soft pink bands, a look visitors call mineral ice cream, and the light bouncing up off the water paints the ceilings blue. Kayaks set out from the village of Puerto Río Tranquilo, twenty minutes across the water, and slip into narrow slots between the outcrops that a motorboat is too wide to enter; the motorboats go further under the arches into the caverns locals call the Chapel and the Cave, deepest in autumn or early spring when the lake has dropped and the hull can nose in.
Waves have worn openings clean through the thinner marble walls, so from inside the caverns you look out through natural windows in the stone at the lake and the mountains, and the free-standing islet in the middle of the water, the Cathedral, is reached at first light before the wind wakes, since the lake is famous for its afternoon gales. The colour is glacial: in high summer the melt loads the lake with rock flour and the sun rides highest, so the water burns its most intense turquoise against the pale marble, and in April and May the lenga forests around the shore turn deep red and gold. The lake belongs to two countries and carries two names, General Carrera in Chile and Buenos Aires across the border in Argentina. The Marble Caves are a piece of seabed the lake has been carving for six thousand years, and the water inside them is the colour of the work.