Putana is the volcano you notice on the way back from El Tatio, because it is visibly alive: a permanent plume of sulphurous steam drifts off the fumarole field near its 5,890-metre summit, catching the morning sun. It sits on the Bolivian border and has not erupted in recorded history, but the degassing has never stopped.
The reason to stop is not the mountain but the ground beneath it. The Vado Putana, where the road fords the river at around 4,200 metres, is a bofedal — a high-altitude peat wetland, bright green against the brown — and it is the best wildlife stop on the northern circuit. Vicuñas graze in numbers, Andean geese and giant coots work the channels, and the occasional culpeo fox turns up on the far bank.
Summit attempts are possible but rare and require a permit and a guide; almost everyone experiences Putana from the road. Tours running the Tatio-Machuca route usually stop here for twenty minutes, which is enough.