Spas with reservation required

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

Miami, Florida

Hotel spa at The Ritz-Carlton Key Biscayne, Miami, with treatment suites, sauna, steam room and whirlpool, open to hotel guests 18 and up by appointment.

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+.

Idaho City, Idaho

A reservation-only hot springs soak in Idaho City with private tubs, a steam room and a $30 day pass, open five days a week.

Miami, Florida

Hotel spa inside Trump National Doral with 42 treatments, couples massages, sauna, steam room, cold plunge and jacuzzi, open daily 9am-7pm.

Philadelphia, Pennsylvania

Hotel spa in Center City Philadelphia with a heated indoor saltwater pool, fitness center and day-pass access for non-guests.

Aspen, Colorado

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

Sedona, Arizona

Adults-only resort spa in Sedona with outdoor hot tubs, steam rooms and a 30-treatment menu, open daily with walk-ins and day passes.

Canggu, Bali

A hotel spa at Theanna Villa in Canggu with a pool, gym, restaurant and shuttle service, open to guests by reservation only.

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

Key West, Florida

A medical spa in Key West offering Morpheus8, injectables and body contouring, with a sauna, steam room and thermal pool on site by appointment only.

Gold Coast, Queensland

A 90-minute hydrotherapy circuit in Southport with a Finnish rock sauna, 5° ice baths and hot/cold magnesium pools, day pass $49.

Scottsdale, Arizona

Adults-only hotel spa at the Fairmont Scottsdale Princess with a rooftop pool, grotto waterfall pool, sauna, steam room and cold plunge, open daily 6am-7pm.

Houston, Texas

A Houston day spa on E Airtex Dr with two locations, offering massage, facials and body treatments alongside a sauna, steam room, cold plunge and thermal pool.

Carmel, Indiana

A moderate-priced day spa in Carmel, Indiana with sauna, steam room and thermal pool, plus facials, massage and body contouring treatments.

Nashville, Tennessee

Upscale day spa in Franklin outside Nashville offering facials, massages, a salt room, infrared sauna and hydrotherapy tub, open daily by reservation.

Houston, Texas

Luxury day spa near Houston's Galleria with massage, facial and body treatments, a salt room and infrared sauna; reservations only, no walk-ins.

Charleston, South Carolina

A 52-treatment luxury day spa in Mount Pleasant near Charleston, with Vichy showers, couples suites and a $370 signature package; reservations required.

The Colony, Texas

A day-soaking spa in The Colony with mineral pools at varying temperatures, seven saunas, cold plunges and a poolside café.

Glenwood Springs, Colorado

A natural geothermal vapor cave in Glenwood Springs, Colorado, where visitors steam in ancient rock chambers and add massages, mineral baths or body treatments.

Park City, Utah

A reservation-only day spa in Sandy, Utah, built around scalp spa treatments, plus sauna, steam, cold plunge and thermal pools.

Portland, Oregon

A moderate-priced day spa in Portland's Irvington neighborhood with massage, facials, couples treatments and Oregon's only halotherapy salt cave.

Miami, Florida

Medical spa in Miami's Edgewater doing Botox, fillers and facials, plus a sauna, steam room and thermal pool for aftercare.

Vail, Colorado

Hotel spa inside Park Hyatt Beaver Creek with a 5-step hydrotherapy circuit, sauna, steam room and day-pass access to massages, facials and fitness classes.