The shape tells the story. Cochamo is a textbook U-shaped glacial valley, its floor scooped flat and its walls planed vertical by an immense glacier that ground through here over the course of millions of years before melting back into the Andes. What the ice left behind is a tiered world: lush green pasture on the valley floor, giving way upward to dense temperate rainforest, then to thickets of native bamboo, and finally to the bare granite domes and peaks that crown the rim. Waterfalls spill down the rock in numbers no one bothers to count, and the streams run clear enough to drink straight from. It is, by any measure, some of the most spectacular landscape in northern Patagonia.

Among Cochamo's true treasures are its alerce trees - Fitzroya cupressoides, a relative of the giant sequoia and one of the longest-living organisms on Earth, capable of standing for over 3,600 years. To walk beneath them is to move among living things that were already ancient when European ships first reached these shores. The rainforest around them is one of only a handful of intact temperate rainforests left in the world, hung with ferns and vines and lit by the bell-shaped, bright-pink copihue, Chile's national flower. The wildlife is shy but remarkable: the pudu, the world's smallest deer, picks through the undergrowth; pumas prowl the upper reaches unseen; and the tiny, critically endangered Darwin's frog - which broods its young inside the male's vocal sac - still survives in this valley when it has vanished from so many others.

The trail through Cochamo has carried traffic for more than a century. Long before tourists, it was the path of gauchos driving cattle, of missionaries, and of the occasional outlaw - local legend holds that the American bandits Butch Cassidy and the Sundance Kid passed this way during their South American years. The valley's modern rediscovery owes much to Clark Stede, a German traveler and journalist who arrived in his small aluminum yacht in the waning years of the Pinochet regime, in the late 1980s. He had meant only to pass through. One look at the granite peaks and he stayed, working with young local huasos to reopen the long-disused trails and bring the first international visitors to a valley the wider world had forgotten.

Today Cochamo's upper basin, called La Junta, is one of the great big-wall rock climbing destinations on the planet. The first routes went up on the Cerro Trinidad wall in the late 1990s, after the climber Crispin Waddy and his partner spent days hacking a trail through the jungle to reach its base in 1997. Since then, climbers have established more than 200 big-wall routes on the valley's domes, and thousands of unclimbed lines still wait. But you do not have to climb to be moved here. Most visitors come on foot or horseback for the waterfalls, the granite arches, the natural rock waterslides, and the chance to meet mountain homesteaders living self-sufficiently as they have for generations. With fame has come strain - more boots, more litter, more pressure on a fragile place - and the open question hanging over Cochamo is whether it can stay this wild now that the world has finally found it.