Acamarachi — also called Pili — rises to 6,046 metres east of the Salar de Atacama, and it is the one on the horizon that looks like a child's drawing of a volcano: a dark, symmetrical cone with no shoulders. That shape is the problem. The final section is steep enough to need hands in places, and the rock is loose, so it is a proper mountaineering objective rather than a walk-up.
Expect a two-day trip with a high camp, a guide, and a hard pre-dawn start. Operators will not take you without evidence that you have acclimatised on something easier first. The reward is the summit shrine, the small crater lake just below it, and a view across to Argentina that takes in half a dozen six-thousand-metre peaks.
Nobody should attempt this independently. The approach tracks are unmarked, the weather turns fast above 5,000 metres, and there is no mobile signal anywhere on the mountain.