This is, and has always been, Mapuche country. Communities still live within the park's boundaries, on land their ancestors held long before Argentina established the park in 1937 to protect these Andean-Patagonian forests, making it the third largest in the country at more than 412,000 hectares. Lanin is unusual in another way too: it is the only national park in Argentina co-managed with the indigenous Mapuche, on whose territory it sits. The forests here are unlike any other. Among the beeches grow the araucarias, the trees the Mapuche call the pehuen and the English-speaking world knows as the monkey-puzzle. These are not ornamental specimens. Their large seeds, gathered each autumn, have fed the Pehuenche people for generations, a staple harvested from the high forest when the carbohydrate-rich nuts ripen. To stand beneath a thousand-year-old pehuen is to stand inside a living larder that has sustained a culture.

More than twenty lakes lie cupped within the park, fed by snowmelt running off Lanin and its neighbors in countless small streams. Lago Huechulafquen, whose name means Long Lake in the Mapuche tongue, is the giant among them, joined to Lake Paimun in the north and Lake Epulafquen in the south, a chain of deep cold water mirroring the volcano on still mornings. Forest crowds the shoreline, the cone floats above it, and the whole composition rearranges itself with the light. The two classic routes up Lanin trace these waters: one begins near Tromen Lake, the other near Huechulafquen, and both demand a permit from Argentina's park authority and a guide who knows the mountain's moods. Few landscapes reward a slow pace this generously.

The park's lakes draw fly fishers from around the world, who come for rainbow and brown trout that run thick in the cold currents. There is an irony worth naming: neither fish belongs here. Both were introduced to Patagonia in the early twentieth century, deliberately stocked into waters where they had no native counterpart, and both thrived so well they became part of the region's identity. Today an entire culture of guides, lodges, and seasons has grown around chasing them. The trout are invaders that the place adopted, a reminder that even a landscape this wild has been quietly reshaped by human hands.

The little town of San Martin de los Andes is the doorway to all of this, a base for backcountry expeditions and a place to hire the local knowledge the mountains require. From here the dirt roads fan out toward trailheads, waterfalls like the Cascada El Saltillo and the Cascada de Chachin, and the climbing routes on Lanin itself; the smaller town of Junin de los Andes, about 45 kilometers north, serves the routes on the volcano's other flank. The setting is improbably scenic, ringed by peaks and lakes, and it has the unhurried feel of a frontier that never quite stopped being one. Cross a pass and you are in Chile, where Lanin's volcanic siblings rise above Pucon and the border becomes a technicality the landscape ignores entirely.