San Pedro has a high concentration of tour operators offering excursions into the surrounding altiplano, all broadly similar and all at pretty much the same price. This can, of course, be a curse as well as a blessing, for it increases tourist traffic in the region to the point where it can be difficult to visit the awe-inspiring landscape of the puna in the kind of silence and isolation in which it really ought to be experienced. Some of the tours are responsibly managed but many are not; the astounding environmental damage of late has finally, if belatedly, forced local communities (but not the national authorities) to take action; they now charge entrance fees to each site and do their best to clean up after visits. The tourist office keeps volumes of complaints registered by tourists (usually concerning reliability of vehicles or lack of professionalism) and they are worth consulting to find out which operators to avoid.
Tours usually take place in minibuses, though smaller groups may travel in jeeps. Don’t necessarily choose the cheapest tour, as some companies cram passengers in and offer below-par services, so it may be worth paying a couple of thousand pesos more. Do visit several companies – or their websites, where available – to get a feel for how they operate and to work out which one you prefer. If you don’t speak Spanish, check that they can offer guides who speak your language (French, German and English are most common languages on offer).