Spas with groups

Saratoga Springs, New York

A floating Nordic-style sauna moored on Saratoga Lake, with a 15-person cabin, roof terrace and lake plunge, open daily except Monday.

Arima Onsen, Hyogo

A moderately priced onsen bathhouse in Arima Onsen, Kobe, with a forest sauna, a large outdoor bath, yoga and an award-recognized restaurant.

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.

Arima Onsen, Hyogo

Hotel spa in Arima Onsen with Arima's rare iron-rich "ginsen" waters, outdoor baths, sauna and jacuzzi, run as an all-inclusive overnight stay.