Spas with moderate

Galway, Connacht

Adults-only hotel spa in Galway with a thermal suite, hydro pool and sauna; day pass runs about €50 and reservations are required.

Aspen, Colorado

Adults-only hotel spa at Viewline Resort Snowmass with a $25 day pass, steam rooms, outdoor pool and whirlpool, reservations required.

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.

Spa, Liège

Thermal baths in the town of Spa, Belgium, fed by natural mineral water, with saunas, hammams and separate textile and naturist relaxation areas.

Palm Springs, California

A 16-room adults-only hotel in Desert Hot Springs with three natural mineral-water pools fed by a 350-foot geothermal well, plus a small on-site spa and

Rogaška Slatina, Savinjska

Wellness center at Grand Hotel Rogaška in Rogaška Slatina, Slovenia, with pools, saunas and fitness; day pass available by reservation.

Hanoi

Day spa in Hanoi's Old Quarter with a herbal steam room, Himalayan salt stone room and jacuzzi, open daily 10am–10pm.

Taupo, Waikato

Adults-only geothermal hot springs in the Wairakei valley near Taupo, with three thermal pools fed by natural silica-rich mineral water, plus spa treatments

Santa Fe, New Mexico

A 16,000-square-foot adults-only hotel spa at Hilton Buffalo Thunder near Santa Fe, with separate men's and women's saunas, steam rooms and whirlpools.

Boston, Massachusetts

A hotel day spa at Battery Wharf in Boston's North End with a co-ed Turkish hammam, separate saunas, and fitness studios for barre and yoga.

Palm Springs, California

Adults-only clothing-optional resort in Desert Hot Springs with mineral water pools, whirlpools, a nude cedar sauna and day-pass access.

Minneapolis, Minnesota

A St. Paul wellness studio in Macalester-Groveland offering infrared sauna, float tanks, salt therapy and cold plunge by reservation, adults-only, day-pass

Calistoga, California

A day spa and co-ed bathhouse in downtown Sebastopol with women-only and clothing-optional sessions on set days.

Sedona, Arizona

Day spa in Sedona with eucalyptus steam rooms, saunas, jacuzzi and a fitness center, offering day passes and memberships for walk-in guests.

Brežice, Posavje

A large thermal water park in Brežice, Slovenia, with a year-round indoor pool riviera, an adults-only sauna zone, and seasonal outdoor slides.

Puelo, Los Lagos

Adults-only hot springs in Puelo with ten thermal pools, a sauna, steam room and individual herbal tubs, open daily with walk-in day passes.

Houston, Texas

Westside Houston day and med spa with treatment menu plus an H-Circle membership for $99/month, open daily with day passes available.

Milan, Lombardy

Adults-only day spa in a Liberty-style building near Milan's Parco Sempione, with thermal pools, saunas, steam room and a hydrotherapy circuit.

Orlando, Florida

A 10,000-square-foot hotel spa at Westgate Lakes Resort in Orlando with massages, facials, sauna, steam room and a fitness studio, open daily.

Santa Fe, New Mexico

A Santa Fe day spa combining yoga, pilates and nia classes with spa treatments, a café and a boutique, open daily 9am–7pm.

Carson, Washington

A clothing-optional, adults-only mineral hot springs bathhouse in Carson, Washington, with a $12 day pass and a $30 bath-and-wrap treatment.

Calistoga, California

A clothing-optional hot springs retreat outside Calistoga with eight mineral pools, spa bodywork, and day-pass, camping, and lodging options.

Miami, Florida

A hotel spa in downtown Miami with a day pass covering sauna, steam, cold plunge and thermal pools, plus 13 treatments on the menu.

San Francisco, California

A Japantown bathhouse open for 50+ years, with a Japanese-style thermal pool and relaxation lounge, reservation required, adults only.