Spas with thermal pool

Lake Tahoe, California

A 17-room, adults-only hotel spa at Lake Tahoe's Ritz-Carlton with a heated lap pool, sauna and steam room; day pass access requires booking a treatment.

Portland, Oregon

Adults-only hotel spa in downtown Portland with a $50 day pass, infinity pool, sauna, steam room and cold plunge shower, booked in advance only.

Naples, Florida

Hotel spa at The Ritz-Carlton, Naples with 23 treatments, steam rooms, plunge pool and separate men's and women's lounges, open daily 9am–6pm.

Naples, Florida

A hotel spa at Naples Beach Club with a 3,200-square-foot thermal circuit, rooftop lap pool and body/facial treatments built around ocean and plant themes.

Santa Ynez, California

Adults-only resort spa inside Chumash Casino Resort in Santa Ynez with 21 treatments, a mineral pool, cold plunge and couple's suites.

Los Angeles, California

Four Seasons hotel spa in Beverly Hills with a steam room, rooftop pool, fitness center and eight treatments, open daily, day passes available.

Napa Valley, California

Adults-only hotel spa in Napa Valley with a co-ed thermal circuit of sauna, steam room and cold shower, open daily 10am–6pm; day passes available.

Palm Springs, California

A 38,000-square-foot resort spa at JW Marriott Desert Springs in Palm Desert offers day passes, saunas, a saltwater lap pool and couples suites.

Atlanta, Georgia

Hotel spa inside the Four Seasons Atlanta in Midtown, open to guests 16 and up for massages, facials and a heated saline pool with sauna and steam room.

Vail, Colorado

A hotel spa at Grand Hyatt Vail with three treatments, an outdoor heated infinity pool, hot tubs and cold plunges along Gore Creek.

Bodrum, Muğla

Adults-only hotel spa at Mandarin Oriental, Bodrum with sauna, steam, cold plunge and thermal pools, open daily 10am-10pm, reservation required.

Napa Valley, California

Adults-only hotel spa in downtown Napa with thermal circuits, sauna, steam and cold plunge, plus massages, facials and medical aesthetics.

San Diego, California

Adults-only day and hotel spa in Rancho Bernardo with gardens, whirlpools, a steam room and an 18-treatment menu, open daily 9am-6pm.

Calistoga, California

A 20,000-square-foot resort spa in Calistoga with five geothermal pools, Calistoga mud treatments, and a day pass for non-hotel guests.

Park City, Utah

A hotel spa at Stein Eriksen Lodge in Park City with indoor/outdoor pools, saunas and cold plunge, open to lodge guests for about eight treatments.

Killarney, Munster

Hotel spa and leisure studio at The Killarney Park with a 20m pool, outdoor jacuzzi, sauna and steam room, open to hotel guests only.

Asheville, North Carolina

Adults-only hotel spa in Asheville with a fiber-optic-starred lap pool, waterfall pools, saunas and an electronics-free policy; day passes are limited and

Calistoga, California

A 20-treatment hotel day spa in Santa Rosa with an indoor caldarium plunge pool, eucalyptus steam rooms, and walk-in or reserved day passes for adults 18+.

Miami, Florida

Adults-only hotel spa on Belle Isle near South Beach with a hammam, sauna, ice room, infinity pool and a day pass option for non-guests.

Whistler, British Columbia

Hotel spa at the Westin in Whistler Village with 19 treatments, couples massage, and free access to the hotel's pools, sauna, steam room and gym.

Bath, England

Adults-only thermal spa in central Bath with a naturally warm mineral rooftop pool, open daily 9am–9pm with walk-in day passes.

Aix-les-Bains, Auvergne-Rhône-Alpes

Medical thermal baths in Aix-les-Bains treating respiratory and oral mucosal conditions with sulfur-rich water, mostly through prescribed multi-day cures.

Dax, Nouvelle-Aquitaine

Family-run thermal hotel in Dax with a supervised pool, sauna, hammam and a 20-treatment mini-cure over five days, plus day-pass access to the spa.

San Pedro de Atacama, Antofagasta

A hotel spa inside the luxury Tierra Atacama lodge near San Pedro de Atacama, with indoor and infinity pools, sauna, steam room and treatment rooms, open only