Spas with reservation required

Palm Beach, Florida

A Palm Beach Gardens studio offering 60-minute private-suite sessions combining infrared sauna, cold plunge and vitamin-c shower.

Charleston, South Carolina

Private contrast-therapy suites with infrared sauna, cold plunge and vitamin C shower in West Ashley, Charleston, by reservation.

Miami, Florida

A 12,000-square-foot hotel spa at Coral Gables' Biltmore, with eucalyptus steam rooms, Himalayan salt saunas and a couples suite; adults-only, reservation

Charleston, South Carolina

A King Street medical spa in Charleston's Harleston Village offering injectables, laser and skin treatments through nurse-practitioner-led membership plans.

New York City, New York

A 30-treatment luxury hotel spa in Lower Manhattan with a lap pool, steam rooms and the German GREEN PEEL facial as its signature service.

Seattle, Washington

Hotel spa in downtown Seattle for Four Seasons guests, with a Himalayan salt wall, steam rooms and a six-treatment adults-only menu.

Park City, Utah

A hotel spa in Park City with seven treatment rooms, hydrotherapy tub and steam rooms, open to guests by reservation, minimum age 16.

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.

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.

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+.

Philadelphia, Pennsylvania

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

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

Merano, Trentino-South Tyrol

An adults-only, guests-only longevity retreat and hotel spa in Merano with a medical-led wellness institute and private suite treatments.

Rogaška Slatina, Savinjska

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

Santa Fe, New Mexico

Hotel spa at the Eldorado in downtown Santa Fe offering massage and bodywork treatments; appointments required, no day pass.

Park City, Utah

A Park City studio pairing private infrared sauna cabins with float therapy tanks, booked by reservation, with membership options for regulars.

San Diego, California

A day spa in University City, San Diego, open since the late 1990s, offering facials, massage and lymphatic drainage with a monthly membership option.

Mariánské Lázně, Karlovy Vary Region

Hotel spa inside Mariánské Lázně's Ensana resort complex, open daily 8am–5pm for guests with reservations.

New York City, New York

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

Philadelphia, Pennsylvania

A second-floor day spa near Rittenhouse Square offering skincare, scalp analysis and its signature Aroma Chakra Balancing Therapy, with a membership discount

Tucson, Arizona

Day spa near Swan Way Park in Tucson with a cedar hot tub, cold plunge, infrared sauna and massage, bookable by reservation for adults only.

Key West, Florida

A hotel spa at Pier House Resort in Key West for guests only, offering couples treatments for ages 14 and up with advance reservations.

Solvang, California

A resort spa inside Alisal Ranch, a 10,500-acre luxury guest ranch in Santa Ynez Valley open only to overnight guests by reservation.

Hudson Valley, New York

Hotel spa at a small Hudson Valley inn on 75 riverside acres in Milton, NY, open to overnight guests by reservation while the spa undergoes renewal.