Spas with solo travelers

Vail, Colorado

Walk-in recovery clinic in Lionshead, Vail offering IV therapy, compression boots, cryo, red light and hyperbaric treatments aimed at skiers and athletes.

Philadelphia, Pennsylvania

A head spa in Queen Village, Philadelphia, focused on scalp and hair treatments, with private suites and a $300 signature service.

Napa Valley, California

Hotel day spa atop the Archer in downtown Napa with a water deck, fitness studio access and treatment rooms; reservations required.

Karlovy Vary, Karlovy Vary Region

A one-room beer bath spa in a 18th-century cellar in central Karlovy Vary, with unlimited beer, oak tubs and a straw-bed rest area.

Seattle, Washington

A clothing-optional outdoor hot pool, sauna and sun deck in Seattle's West Woodland, open to walk-ins for three-hour day visits.

Denver, Colorado

A Denver day spa in Speer built around the Vietnamese Red Dao herbal bath, with infrared sauna, salt chamber and foot baths, open daily 10am-6pm.

Seattle, Washington

An adults-only wellness studio near Green Lake with private infrared sauna suites, therapeutic massage and red light therapy by reservation.

Sedona, Arizona

A moderately priced day spa in Sedona with outdoor gardens, a hot tub and fountains, known for its Prickly Pear Pomegranate body treatment.

Asheville, North Carolina

A Japanese-inspired destination spa on a mountainside outside downtown Asheville, built around private outdoor salt hydrotherapy tubs and massage.

Santa Barbara, California

A downtown Santa Barbara day spa built around a private infrared sauna, salt room, cold plunge and a sound-and-light meditation pod, booked by appointment.

Aix-les-Bains, Auvergne-Rhône-Alpes

An upscale day spa inside Hotel Le Riviera in Aix-les-Bains, with pools, saunas, a hammam and eight treatment rooms open to walk-ins.

Naples, Florida

Upscale day spa in Naples offering infrared sauna, massage, facials and foot detox, with a $230 signature massage and couples packages.

Nashville, Tennessee

A Germantown contrast therapy studio with private suites pairing infrared sauna, cold plunge and a vitamin-c shower; day pass is $70.

Charleston, South Carolina

Contrast therapy studio in Mt Pleasant offering private 60-minute sessions with infrared sauna, cold plunge and vitamin-c shower; day pass $60.

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.

Ibusuki, Kagoshima

Oceanfront outdoor onsen in Ibusuki where the two gender-assigned baths swap daily, with views of Mount Kaimon, the East China Sea, and Take-yama.

Taos, New Mexico

Hotel day spa at El Monte Sagrado in Taos with a hydrotherapy circuit, saltwater pool and treatment rooms, open daily, day passes available.

Calistoga, California

Hotel spa in downtown Healdsburg with a garden patio, jacuzzi and pool access, open daily 9am-5pm for guests and day visitors.

Los Angeles, California

Four Seasons hotel spa in Beverly Hills with a steam room, rooftop pool, fitness center and eight treatments, open daily, day passes available.

Houston, Texas

A Four Seasons hotel spa in downtown Houston with three treatment rooms, a couples' suite and rooftop pool access, open to day-pass guests.

Milan, Lombardy

A luxury hotel spa inside Four Seasons Hotel Milano with a 14-metre pool under a vaulted ceiling, sauna, gym and private suites for couples' treatments.

Chicago, Illinois

A 5th-floor day spa inside the Palmer House Hilton in the Loop, built around a hydrotherapy circuit, Vichy shower treatments and a facial called Glow Revival.

San Diego, California

Resort spa on Mission Bay offering massages, facials and body treatments, with walk-ins welcome and a gym and yoga classes on-site.