Hot mineral springs beneath downtown Paso Robles gave the town its early identity as a health resort. Several hotels and spas still draw on the geothermal water, though the therapeutic frenzy of the late 19th century has largely given way to wine tourism. The Paso Robles Inn, on the site of the original 1864 hotel, has individual outdoor soaking tubs fed by the springs in some of its rooms.
If you are staying in Paso Robles for a few days, a soak in the mineral water makes a pleasant counterpoint to the wine tasting. The water temperature and mineral content (sulphurous, saline) are genuinely therapeutic, or at least relaxing. The Franklin Hot Springs facility offers day access for those not staying at the inn.