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.

London, England

A Russian-style banya bathhouse in Belgravia offering oak-lined steam rooms, cold plunge pools and leaf-massage rituals, with day passes by reservation only.