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.

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.

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.

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.

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.

Oslo

Waterfront sauna spot on Aker Brygge with shared and private saunas, sea bathing, and sauna boat trips on the fjord.

Boston, Massachusetts

A Finnish kelo-log banya in Newton with sauna, steam room and cold plunge, alternating men's and women's days, day passes from $69.

Phuket

Adults-only Ayurvedic resort on a Rawai hillside with doctor-led Panchakarma programs, a saltwater pool and 47 private villas.

Amsterdam, North Holland

A small Amsterdam-West studio offering one-on-one Ayurvedic and deep tissue massage, with both walk-in and reservation options.

Sedona, Arizona

Namti is an Ayurvedic day spa in Sedona offering six treatments, including a $129 Abhyanga massage, with walk-ins and couples sessions available.

Hudson, New York

Adults-only communal thermal baths and steam room in downtown Hudson, NY, with day passes, memberships and treatment-plus-soak packages.

Rishikesh, Uttarakhand

A compact Ayurvedic spa and yoga retreat near Laxman Jhula in Rishikesh, offering six treatments including Shirodhara by appointment only.

Denver, Colorado

A small European-style bathhouse in Denver where you rent a private sauna by the hour and share a cold plunge, cold waterfall bucket and steam room.

Nashville, Tennessee

A community sauna studio in East Nashville's Porter Road corridor with communal and private sauna rooms plus an outdoor pop-up cold plunge.

Saratoga Springs, New York

Historic 1935 bathhouse in Saratoga Springs offering mineral water soaks and massages in original tubs, reservation only, moderate pricing.

Budapest

A centuries-old Turkish-style thermal bath on the Buda riverside with pools, saunas, massages and weekend late-night soaking hours.

Cotswolds, England

A woodland sauna and ice bath venue near Northleach in the Cotswolds, offering communal and private heat-and-cold sessions plus occasional workshops.

Mumbai, Maharashtra

An upscale Ayurvedic retreat in Vile Parle West, Mumbai, with five treatments, couples rooms and a relaxation lounge; reservations required, open daily

Piešťany, Trnava Region

Spa Irma on Piešťany's spa island offers historic mud and mirror thermal pools, a hydrotherapy circuit and a 60-treatment medical spa menu, adults only.

Frisco, Texas

An Ayurvedic wellness center in Frisco offering oil massage, shirodhara, dosha consultations and detox packages, led by practitioner Ritu Bhalla.

Bad Wörishofen, Bavaria

Adults-only thermal baths in Bad Wörishofen with palm-house pools, mineral pools and saunas; day passes available, minimum age 16.

Chianciano Terme, Tuscany

Thermal day spa in Chianciano Terme offering day passes, couples massages and a wellness-food menu, closed Thursdays and Wednesdays.