Cerro Castillo is crowned by a row of dark basalt towers so like the turrets of a castle that Chile named the whole mountain Castle Hill. They rise to 2,675 metres in the Aysén region of Patagonia, right beside the Carretera Austral, the rough highway that runs the length of Chile's south. A hanging glacier clings to the face below the summit, and its meltwater feeds Laguna Cerro Castillo directly underneath. The lagoon is deep turquoise because glacial silt, ground as fine as flour, hangs in the water and scatters blue light back at you. Ice breaks off the glacier now and then with a crack that echoes off the walls. The peak crowns a park of 138,164 hectares, protected since 1970 and raised to national-park rank in 2017. For years it stood in the shadow of Torres del Paine to the south; the rock walls here rival that skyline and draw a fraction of the visitors.
Most people come for the mirador above the lagoon, a stiff six-to-seven-hour day hike from the highway through beech forest and loose scree. Those with more time walk the four-day Las Horquetas traverse, roughly 50 kilometres past hanging glaciers and mountain lagoons the day-hikers never reach. Campsites on that route book out well ahead in summer. The wind rarely stops; it whistles through the stones and bends the low beech permanently to one side. This is huemul country: the deer on Chile's coat of arms still browses the treeline here, and condors ride the currents above the towers. On clear nights, far from any town, the sky fills with stars. Cerro Castillo is still one of Patagonia's least-crowded great mountains, reached along the Carretera Austral rather than by any easy road.