Spas with reservation required

London, England

Thermal bathhouse near Covent Garden in a former J.M. Barrie house, offering multi-temperature pools, massages and couples treatments by reservation.

Toronto, Ontario

A reservation-only thermal bath circuit in a 1912 Edwardian building in Toronto, with eight pools, a dry sauna, steam room and massage treatments.

Amsterdam, North Holland

A day spa inside a former bank vault in central Amsterdam, with pool, whirlpool and a canal-view gym; adults-only, day pass by reservation.

Santa Fe, New Mexico

A small medical spa in Santa Fe focused on advanced facials, skin rejuvenation and massage, by reservation.

Barcelona, Catalonia

Adults-only thermal baths in a converted 18th-century building near Barcelona's Born market, with soaking pools, massages and couples rituals.

Copenhagen, Capital Region

A thermal-bath spa in Vesterbro, Copenhagen, built around a signature Pediluvium foot-bath ritual plus a relaxation lounge and thermal pool.

Chicago, Illinois

Reservation-only day spa in Chicago's River North/Goose Island area with massage, facials and body treatments, plus a chakana-shaped tented relaxation room.

Houston, Texas

Island-themed day spa in Montrose offering massage and body treatments by appointment only, with no walk-in day pass.

Sonoma, California

A Sonoma medical day spa run by a 25-year skincare specialist, offering non-toxic facials, microcurrent and micro-channeling treatments up to $350.

Nashville, Tennessee

A Midtown Nashville spa inside Sola Salons that does one thing: head spa treatments combining scalp massage, warm water, steam and a finishing blowout.

Längenfeld, Tyrol

A large thermal bath and 4-star hotel spa in the Ötztal valley near Längenfeld, with indoor-outdoor pools, a sauna garden and a dedicated kids' water world.

Singapore

Garden-set day spa inside Bishan Park 2 with 12 treatment rooms, outdoor baths, massages and facials using Elemis and Skinceuticals products.

San Francisco, California

Adults-only Russian bathhouse in San Francisco's India Basin with steam rooms, cold plunge, rooftop deck and a café, open daily except Tuesday.

Daylesford, Victoria

A rammed-earth house on 80 hectares near Daylesford, rented whole for up to 10 adults, with in-room massage and a two-night minimum stay.

Sydney, New South Wales

Reservation-only Korean bathhouse in Paddington, Sydney, with herbal baths, a steam room and the signature Korean Body Scrub, closed Tuesdays.

Asheville, North Carolina

A therapist-owned day spa near downtown Asheville offering massage, bodywork, a private sauna and foot soaks by appointment, with free parking.

Asheville, North Carolina

A downtown Asheville salt cave with Himalayan salt walls, a hammam steam bath and massage rooms for solo visitors and couples, reservation-based.

Aspen, Colorado

A reservation-only Aspen studio offering private sound, energy and subconscious-journey sessions instead of classic spa treatments.

Hot Springs, Arkansas

Adults-only hotel spa at Oaklawn Resort in Hot Springs with vitality pools, heated loungers, needle showers and treatment-based access only.

Las Vegas, Nevada

Adults-only hotel spa at Resorts World Las Vegas with a six-pool hydrotherapy circuit, salt room, and a themed Aufguss sauna show on weekends.

Palm Springs, California

Adults-only hot springs resort on Miracle Hill in Desert Hot Springs with private mineral tubs, a Finnish sauna, salt room and 35 spa treatments.

Seattle, Washington

Japanese head spa and beauty studio in Seattle's Junction neighborhood, open by appointment Tuesday through Saturday.

Seattle, Washington

A private floating bathhouse on Seattle's Lake Union, booked out entirely for one group of up to 12 for sauna, cold plunge and hot tub rounds.

Austin, Texas

Medical spa and day spa on South Lamar offering facials, injectables, massage and a signature $1,499 Mermaid Lift, open daily with private rooms and a stocked