The Puritama hot springs sit in a narrow canyon about 30 kilometres north of San Pedro, at 3,500 metres. Eight pools step down the floor of the gorge, linked by wooden walkways and fringed with reeds, each one fed by the same geothermal stream at a steady 33°C. It is warm rather than scalding — you can stay in for an hour without going pink — and the canyon walls block the wind, which matters more than you would think at this altitude.
This is the most expensive single thing most people do around San Pedro. The site is privately run and the entrance fee is in the region of 35,000 pesos, with a cheaper afternoon rate; tours from town add transport on top. Go early if you want the upper pools to yourself, because the tour minibuses arrive in a block mid-morning and the lower pools fill up first.
A word on the alternative: a few kilometres downstream, where the thermal water rejoins the Río Puritama, there are rough unmanaged pools that locals call Purilibre. They are free, they are much cooler, and there are no walkways, changing rooms or lifeguards. Plenty of people prefer them. Getting there needs your own vehicle.