Spas with thermal pool

A resort spa in Tucson's Starr Pass area with a saline lap pool, sauna and fitness center, plus signature treatments from $159 for hotel guests.

Day spa in Allisonville, Indianapolis with sauna, steam room, thermal pool and cold plunge, plus about 10 massage and facial treatments for solo visits or

North Scottsdale day spa with massage, facials, sauna, steam and a thermal pool, plus private suites for couples and groups.

Hotel spa at the Inn at Eagle Mountain in Fountain Hills with sauna, steam room, pools and a $69 60-minute massage as its signature treatment.

An adults-only wellness retreat on Ubud's Ayung River offering multi-day healing programmes, thermal circuits and plant-based cuisine by reservation only.

Day spa in Tucson's La Encantada shopping center with a thermal circuit of sauna, steam room, cold plunge and soaking pools.