Spas with reservation required

A no-frills contrast therapy studio in Carmel, Indiana, built around a 30-minute sauna-and-cold-plunge circuit for solo visitors.

A no-frills massage studio in North Dallas offering Swedish, deep tissue and its own signature treatment, plus in-home and office visits by appointment.

A medical spa in Chicago's Lincoln Park offering Botox, dermal fillers, laser hair removal, IPL and semaglutide weight-loss treatment, priced in the moderate

East Town Spa in Milwaukee's Juneau Town combines a full-service salon and med spa with a thermal circuit of sauna, steam, pools and cold plunge.

A no-frills massage and facial day spa on West Flamingo Road in Las Vegas, open daily 10am to 8pm with walk-in and reservation options.

A day spa and wellness center in South Jordan, Utah, with a salt room, infrared sauna, cold plunge, float therapy and a yoga studio.

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

Float Horizen is a day spa in Nashville's East End offering sensory-deprivation float tanks, infrared sauna, massage and sound meditation sessions.

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

An adults-only medical day spa in Colorado Springs offering constitutional hydrotherapy, infrared sauna and homeopathy by appointment.

A Thai massage day spa in Honolulu's McCully-Moiliili area offering solo and couples treatments daily from 9am to 11pm.

A Clairemont wellness studio in San Diego pairing acupuncture and bodywork with an infrared sauna and a Himalayan salt room for classes.

Adults-only day spa in Maplewood, NJ, offering deep tissue massage, bodywork and facials by appointment, open daily 9am-8pm.

Day spa in Richmond's West End with massage, organic facials, HydraFacial, infrared sauna and herbal bath soaks; walk-ins welcome, reservations recommended.

All-inclusive multi-night wellness retreat in Pisgah Forest, NC, combining fitness classes, spa treatments, guided hikes and farm-to-table meals in private

A moderate-priced day spa in Minnetonka with a sauna, steam room, thermal pool and cold plunge, set up for couples and adults-only visits.

A moderate-priced day spa in Charlotte's SouthPark area with a sauna, steam room and thermal pool alongside massage, facial and body-treatment menus.

Day spa in Pasadena offering facials, scalp therapy and body treatments, with its signature Synergy Rejuvenation Scalp Spa, open daily 10am-7pm.

A North Raleigh day spa specializing in the Kranial Flush, a scalp and cranial treatment, alongside body work, face and hair therapy.

A single-room salt cave in a Carmichael strip mall offering 45-minute salt therapy sessions for relaxation and respiratory relief.

Medical spa in Northside Jacksonville offering facials, body contouring and VelaShape treatments, open daily except Sunday with reservations recommended.

A medical spa in Brickell's Latitude One building offering Botox, IPL photofacials, body contouring and massage by appointment.

A downtown Napa day spa offering massages, facials, body treatments, waxing and nail services a short walk from the town's restaurants and hotels.

A reservation-only day spa on El Camino Real in San Bruno specializing in head spa therapy, scalp care and lash services for adults.