Unlike the hot pools in Glenwood Springs, this spa doesn’t chlorinate the water, allowing the heady mix of sulfates, chlorides, magnesium and other minerals to soothe bathers just as it has done for generations. The 24 pools have been enclosed by cement and tile and are separated by temperature, ranging from 95°F (35°C) to a deeply satisfying, if challenging, 112°F (44.4°C).

As at most modern facilities of this kind, there’s an added menu of spa options: body wraps, facials, massages and the like. For those who want to spend the night, there is a lodge on hand with clean, comfortable motel-style facilities (rooms from $108 to $195). You get two free days of access to the pools with your stay.