Spas with thermal pool

Barcelona, Catalonia

Adults-only thermal baths in a converted 18th-century building near Barcelona's Born market, with soaking pools, massages and couples rituals.

Amman

A hotel hammam in Tla al-Ali, Amman, with marble bathing halls, a hot pool, sauna and Jacuzzi, offering about 20 treatments from a basic scrub to a $120

Saint-Malo, Brittany

A three-in-one day spa in Saint-Malo combining a salt-water aquatic circuit, spa treatments and a fitness club, open daily on a day-pass basis.

Washington, D.C., District of Columbia

A multi-level day spa near DC with indoor and rooftop hydrotherapy pools, several sauna types, lounges, an a la carte spa menu and eateries.

Miami, Florida

Day spa in the Sherry Frontenac Hotel's lower lobby in Miami Beach, with sauna, steam, cold plunge and thermal pool alongside massage treatments.

Kuala Lumpur

An onsen-style day spa in Kampung Baru, Kuala Lumpur, with thermal pools, sauna, steam room and couples treatments.

Hammamet, Nabeul

Seafront thalasso spa in Hammamet Est with a thermal pool, 42 treatments, and day passes open daily from 8am to 7pm.

Houston, Texas

A Houston day spa near Memorial Park focused on massage and bodywork, with a spa pool, sauna and outdoor retreat, open daily 10am-8pm.

Napa Valley, California

A boutique day spa in downtown Napa Valley with nine treatment rooms offering massage, facials and body work, plus sauna, steam and a thermal pool.

Plainfield, Indiana

Day spa in Plainfield, IN offering facials, massages and body-sculpting treatments alongside a sauna, steam room and thermal pool, reservation required.

Prague

A day spa near Wenceslas Square in Nové Město offering massages, facials and thermal pool access with day passes for walk-ins.

Quito, Pichincha

A family-friendly day spa in Conocoto, just outside Quito, with a thermal pool and a $16 day pass, open daily from 9am to 9pm.

Da Nang

A Korean-style bathhouse and onsen complex in Da Nang's Hoa Xuan area, with hot spring baths, 11 sauna rooms, massage and a riverside restaurant.

Strongsville, Ohio

Membership-style wellness studio in Strongsville with sauna, steam room and thermal pool, plus a $49 unlimited day pass for first-time visitors.

Wiesbaden, Hesse

Historic thermal-water day spa inside Wiesbaden's Hotel Schwarzer Bock, with sauna, steam room, pool and day passes for solo visitors, couples and groups.

Florence, Tuscany

A 650-square-meter spa inside a 14th-century Florence monastery, with thermal pool, guesthouse rooms, bistro and day-pass access.

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 Beach, Florida

A 42,000-square-foot hotel day spa in Manalapan with a central dipping pool, garden lounge areas, and day passes open to non-guests.

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.

Noosa, Queensland

Day spa on Hastings Street in Noosa Heads with a hydrothermal circuit, day passes, and walk-ins welcome.

Scottsdale, Arizona

Day spa in South Scottsdale focused on facials and a signature holistic massage, with sauna, steam room, thermal pool and cold plunge on site.

Monroe, New Jersey

Affordable day spa in Williamstown, NJ with sauna, steam room and thermal pool, offering massages, facials and couples treatments.

Columbia, Maryland

A luxury medical and day spa in Columbia's Town Center combining facials, massage and laser/injectable treatments with a thermal pool, sauna and steam room.

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.