Aire Ancient Baths takes the concept of Roman thermal bathing and places it inside a beautifully restored underground London cellar. The pools are candlelit, the temperature journey is properly considered, and the whole thing operates at a hushed, meditative pace that's genuinely rare in this city.
It's expensive, but it's one of those experiences where the price feels appropriate to what's being offered. Book months ahead for weekends, it sells out fast.