Spas with thermal pool

Jūrmala

A pool-and-sauna complex inside Pegasa Pils Hotel in Jūrmala, with a 12.5m pool, three saunas, steam room and a salt room; day passes available, minimum age 16.

Palm Springs, California

Moroccan-themed inn in Desert Hot Springs with natural mineral hot springs, a spring-fed pool and day-pass access from 9am to 4pm.

Vail, Colorado

Adults-only day spa at The Charter at Beaver Creek with saltwater pools, steam room, sauna and a day pass for treatments or facility access.

Pärnu, Pärnu County

Thermal bath complex in Pärnu with pools, saunas and hot tubs, open daily 7:30–21:30, day passes from €15 on weekdays.

Houston, Texas

Day spa in Houston's Westside with a grotto pool, outdoor pool, steam rooms and sundeck, plus an on-site restaurant; walk-ins welcome.

Tuscany

Hotel spa inside Florence's Four Seasons, with a walled garden pool, whirlpool, sauna, steam room and couples suite, open to day-pass guests.

Temescal Valley, California

Adults-only hot springs resort in Temescal Valley with 19 outdoor mineral pools, red clay baths, and a cave-like grotto, open daily 9:30am-5pm.

The Hamptons, New York

Oceanfront resort spa in Montauk with a seawater and marine-based treatment menu, hydrotherapy, contrast bathing, and a heated saltwater pool.

Napa Valley, California

Resort spa at Stanly Ranch in Napa Valley offering hyperbaric oxygen therapy, cold plunge, sauna, steam room and salt therapy, with day passes available.

Tucson, Arizona

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.

Mallorca, Balearic Islands

A clifftop luxury hotel spa near Cas Català-Illetes with an infinity pool, relaxation pool and a seasonal Spa Bodyna, open to day visitors as well as guests.

Opatija, Primorje-Gorski Kotar

A 5-star hotel spa in Opatija with a sauna centre, seawater pools and couples treatments, open only to Hotel Ambasador guests.

Krynica-Zdrój, Lesser Poland

Mountain resort spa in Krynica-Zdrój with indoor and outdoor pools, a sauna complex, and a clothing-optional 18+ zone; day passes available.

Portorož, Coastal-Karst

Hotel spa on Portorož's seafront promenade with heated seawater and thermomineral pools, open to day visitors as well as hotel guests.

Velingrad, Pazardzhik

Hotel spa in Velingrad with mineral-water pools, saunas, steam rooms and a hammam spread over 4,000 square metres; day passes are available.

Houston, Texas

Upscale day spa at The Houstonian in Houston with 22 treatment rooms, soaking pools and a sundeck; pool access comes with a 50-minute-plus treatment, not a

Bük, Vas

Hotel spa in Bükfürdő with pool, jacuzzi, saunas and massage services, open to guests staying in either of its two linked wings.

Reykjavik, Capital Region

Eight oceanfront geothermal pools in Hvalfjörður, 45 minutes from Reykjavík, plus steam baths, a bistro and guest houses for rent.

Zurich

Thermal baths and rooftop infinity pool set in a former Zurich brewery's historic vaults, with a Roman-Irish spa ritual and day-pass access.

Duluth, Georgia

A 24-hour Korean bathhouse in Duluth with a $30 day pass, sauna rooms, cold plunge, thermal circuits and a junior Olympic pool.

Bad Kissingen, Bavaria

Thermal bath and sauna park in Bad Kissingen with 10 indoor/outdoor pools, nine saunas and a day pass around €40.

Florence, Tuscany

Hotel spa inside the Helvetia & Bristol in central Florence, with two heated pools, a calidarium, sudatorium and tepidarium, open daily to walk-ins and hotel

Lake Como, Lombardy

A day spa inside the Castello di Casiglio parkland near Erba, offering a 3-hour pass with heated indoor-outdoor pools, saunas and a Turkish bath; adults and

Tucson, Arizona

Hotel spa at the Westin La Paloma Resort in Tucson offering massages, facials and body treatments, open only to resort guests.