Almost every agency on Caracoles sells the Valle de la Luna and the Tatio geysers. Vulcano sells altitude: Cerro Toco, Láscar, Sairecabur, Ollagüe, Acamarachi, Aucanquilcha and Licancabur, from 5,600 m up to 6,176 m. They have been doing it since 1998 and hold ANGM mountain-guide and wilderness first-responder certification, which in a town this loosely regulated is worth checking for.
Cerro Toco is the one to start with — 80,000 pesos a head, all in, including the 60 km 4x4 run from San Pedro, about an hour and a half each way. It is a straightforward walk on scree from a high trailhead, and it is the honest way to find out how your body handles 5,000 m before you commit to anything harder. From the rim you look across at the east wall of Licancabur and down over the whole Salar de Atacama.
They publish no street address and no telephone. Quotes and bookings go through WhatsApp, on a number they also print in plain text in the footer.
They also keep an inventory of a hundred things to do in and around San Pedro, which is the most complete list of the area anyone has made in any language and is the source of a good many of the pages in this guide. It is one of the six sites in 6 Blogs for San Pedro and the Atacama.