Arctic Bath, Sweden

This floating nest complex by architect Bertil Harström and Johan Kauppi and is anchored on the Lule River, 30 miles outside the Arctic Circle. Sauna and treatment rooms circle a central cold-plunge pool, while bedrooms are set across in six outlying cabins. Starting from £505 per night, they sleep two and are designed with couples in mind. Interiors are pared back to the very basics: expect a wood-burning stove, a bed and skylight for star-gazing.