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.

Oslo

Waterfront sauna spot on Aker Brygge with shared and private saunas, sea bathing, and sauna boat trips on the fjord.

Port Douglas, Queensland

Ayurvedic-style massage and bathhouse studio in Port Douglas offering couples treatments, yoga and reformer Pilates, bookings required with no walk-ins.

Cotswolds, England

A wood-fired riverside sauna at Whichford Mill in the Cotswolds, with a cold-plunge bath, river dipping, and both private and communal sessions.