Spas with hot tub

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.

New York City, New York

A small Japanese-style bathhouse near Union Square with sauna, hot-tub onsen, cold plunge and a recovery lounge, open by reservation only.

Calistoga, California

A 25-room Sonoma hotel in Forestville with a spa barn offering sauna, steam and pools, mainly for overnight guests.

Kyle, Texas

A 88-acre Hill Country resort near Kyle and Wimberley with overnight rooms, a garden spa, pool, hot tubs and day-pass access by reservation.

Philadelphia, Pennsylvania

A private-reservation spa in Philadelphia's Manayunk neighborhood for date nights, birthday and bachelorette parties, with hot tub, sauna and massage chairs

Denver, Colorado

Adults-only bathhouse on West Colfax Ave in Denver with a steam room, sauna, hot tub and relaxation lounge, open daily except Tuesday.