The three mummies -- a 15-year-old girl called La Doncella, a 7-year-old boy called El Nino, and a 6-year-old girl called La Nina del Rayo -- were found buried in partially natural, partially excavated pits near the summit. They sat in the positions in which they had died, wrapped in fine textiles, their faces composed. The children came from high-status families and were well nourished. They had been brought thousands of kilometers to this mountain for a ritual sacrifice known as capacocha, offered to appease the gods or mark significant events like the death of an emperor. Most likely they were rendered unconscious before being suffocated or left to die in the freezing altitude. A total of 145 objects accompanied them: gold and silver statues, pottery, coca leaves, Spondylus shell figurines, and wooden vessels. La Nina del Rayo had been struck by lightning at some point after burial, damaging her remains, but the other two are among the best-preserved pre-Columbian mummies ever discovered. They now reside in the Museum of High Altitude Archaeology in Salta, Argentina.

The Inca did not simply climb Llullaillaco. They built an infrastructure of devotion. Three roads converge from the surrounding salt flats at a tambo -- an inn with numerous buildings -- at roughly 5,200 meters on the northeastern flank. From there, a ceremonial path ascends the volcano, marked by wooden posts and stone cairns so it could be followed even under snow. Waystations with shelters and protecting walls punctuate the route at progressively higher elevations. The path splits at a point called the Portezuelo del Inca, with one branch continuing to the summit and another to the platform where the children were buried. These are not simple footpaths but engineered routes with retaining walls, defined edges, and staircases. They connect to the major north-south Inca road linking San Pedro de Atacama to Copiapo. About forty-five structures have been identified on the mountain, forming one of the most significant archaeological complexes in the Andes. The entire site was declared a UNESCO World Heritage Site in 2014.

Llullaillaco formed during the Pleistocene in two distinct stages. The oldest rocks date to roughly 1.5 million years ago. During the first stage, lava flows extended up to 20 kilometers from the summit, building the bulk of the edifice that still makes up about 70 percent of its surface. About 150,000 years ago, the volcano's southeastern flank collapsed in a massive debris avalanche that traveled up to 25 kilometers from the summit, covering 165 square kilometers with volcanic rubble. The second stage produced younger, better-preserved lava flows and the summit cone with its conspicuous reddish-black lava tongues. Three prominent lava flows descend from the summit, their fronts up to 60 meters thick. The youngest dated rocks are only 930 years old. Unconfirmed reports describe eruptions in 1854, 1868, and 1877, making Llullaillaco the highest historically active volcano on Earth.

Despite conditions among the harshest on the planet -- intense UV radiation, daily freeze-thaw cycles, and soils nearly devoid of organic matter -- life persists on Llullaillaco. Between 4,400 and 4,900 meters, a sparse steppe of cushion plants and shrubs clings to the slopes, reaching maximum density of about 12 percent ground cover. Above 5,200 meters, vegetation disappears entirely. At the very summit, microorganisms survive in soils so extreme that they have been compared to Martian conditions. Lago Llullaillaco, a frozen lake at roughly 5,500 meters on the northwestern flank, is one of the highest lakes in the world and hosts algae and bacteria. Most remarkably, a population of the Punta de Vacas leaf-eared mouse lives on the volcano at elevations that make it the highest-altitude permanent vertebrate population known to science.

The first recorded Western ascent came in 1952, when Chileans Bion Gonzalez and Juan Harsheim reached the summit. But the Inca had climbed it centuries before them, building on the mountain with primitive technology at altitudes that challenge modern mountaineers equipped with supplemental oxygen. The easiest route follows the ancient Inca path up the northeastern flank, accessed from Chile through the Salar de Punta Negra. Climbers face intense UV radiation, oxygen levels roughly half those at sea level, sudden blizzards, and hypothermia. Until 2006, reports of landmines from border conflicts added another hazard. The volcano rises roughly 2,500 meters above the surrounding terrain, its snow-patched summit visible from Cerro Paranal nearly 190 kilometers away through the crystalline desert air. Llullaillaco National Park, a Chilean protected area established in 1995, encompasses the western slopes, though air pollution from the nearby Escondida copper mine threatens the fragile ecosystems within.