At the foot of Osorno, a volcano of near-perfect symmetry standing 2,652 metres between two lakes in southern Chile, the river is running through what the mountain threw down. An old lava flow off Osorno crossed the outflow of Lake Todos los Santos and hardened into black basalt. The Petrohué has been cutting into it ever since, so the river arrives at a maze of narrow chutes and drops through a dozen falls at once, glacial green over dark rock. Wooden walkways thread the forest and put you on overlooks above the water. The noise drowns out conversation and cold mist drifts over the rail onto you. From the shore at Ensenada, on the other lake, the cone stands directly across the water and doubles in it on a windless morning. Llanquihue is big enough that a breeze from any direction breaks the image, so the still hour after dawn is the reliable one.
A covered chairlift climbs from the ski base over slopes of black scoria and old snow to a platform well below the ice cap. From up there you have the two lakes on either side of the cone, one green, one deep blue. Above it the mountain turns to bare glacier, and the crater is about six hours up on snow that steepens the whole way, roped and with a guide. Charles Darwin watched Osorno erupt at night from the Beagle in 1835, and when an earthquake levelled Concepción weeks later he read the two as one underground force. The volcano has been quiet since 1869. No road was ever cut along Todos los Santos, so the way east is still by water. A catamaran carries you the green length of it from Petrohué to Peulla, a settlement no road reaches, the shores on either side too steep to walk. Back at the falls the two banks are not even the same rock. The river cuts through Osorno's own lava on one side, and the steep bank opposite is the coarse, granite-like rock the volcano was built on.