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.

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.

San Francisco, California

A Japantown bathhouse open for 50+ years, with a Japanese-style thermal pool and relaxation lounge, reservation required, adults only.