Four Seasons Hotel London at Park Lane

The Four Seasons put its spa on the tenth floor, which means you sweat with daylight and rooftops instead of in a basement — a small thing that makes a big difference. The dry sauna and steam room sit within a calm, glass-wrapped wellness floor that feels open and bright in a way London spas rarely manage. It's quietly one of the best-kept secrets among Mayfair hotels: serious facilities, minus the see-and-be-seen energy. The hotel delivers exactly the polished, anticipatory Four Seasons service you'd expect, with large, beautifully kept rooms. For a daytime heat session with actual natural light and a city view, it's a real standout. Guest access to the sauna and spa is included; confirm the spa's opening hours, which are generous but worth checking for early risers.