Spas with reservation required

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.

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.

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.