Most of the hot springs are within private establishments (Spas or Hotel) where you need to buy an entrance which will give you access to dressing room, showers and other services. Check the websites below for access conditions, rates and opening times.
Here all the closest thermal baths to Montepulciano and estimated driving time.
CHIANCIANO TERME (about 20 min)
Recently renovated SPA and hot spring complex with easy access and parkingOfficial website: https://www.piscinetermalitheia.it/en/