Spas with membership available

A walk-in sauna-and-cold-plunge studio in Park City with a 198°F cedar sauna, 40° and 50°F plunge pools, and $39 day passes.

An upscale day spa on Miracle Mile in Coral Gables with sauna, steam room and cold plunge, known for a $200 signature treatment and couples packages.

A Birmingham, Michigan day spa built around waterless volcanic rock treatments, with V-steam, facials, massage and a steam room for adults and couples.

Hotel spa at the Inn at Eagle Mountain in Fountain Hills with sauna, steam room, pools and a $69 60-minute massage as its signature treatment.

Day spa in Sedona with eucalyptus steam rooms, saunas, jacuzzi and a fitness center, offering day passes and memberships for walk-in guests.

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