Spas with moderate

Krynica-Zdrój, Lesser Poland

Mountain resort spa in Krynica-Zdrój with indoor and outdoor pools, a sauna complex, and a clothing-optional 18+ zone; day passes available.

Denver, Colorado

A 6,000-square-foot hotel spa in downtown Denver's Granite Tower, open to day-pass visitors 18 and older for $40 to $75.

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

Rogaška Slatina, Savinjska

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

Carson, Washington

A clothing-optional, adults-only mineral hot springs bathhouse in Carson, Washington, with a $12 day pass and a $30 bath-and-wrap treatment.

Nashville, Tennessee

A hotel wellness area at Sheraton Music City near Nashville airport, open to guests 21 and up, with sauna, steam room, pools and a whirlpool.

Las Vegas, Nevada

Adults-only hotel spa inside Harrah's Las Vegas with steam room, sauna, hot tub and fitness center, open daily with set hours for guests.

Johnson City, New York

A 21-and-over hotel in Johnson City, NY, with a sauna, hot tub and fitness center for guests staying at the property.