Aman New York

If money is no object and quiet is the whole point, this is the one. Aman built a three-storey spa inside the Crown Building and treated heat like a serious discipline — a dry sauna, a steam room, and a 20-metre pool lit like a temple, all hushed to the point of reverence. It is the rare Midtown room where you genuinely forget Fifth Avenue is roaring twelve floors below. The crowd is monied and discreet; the staff anticipate things before you do. It is not cheap and it does not pretend to be — but if you want the most considered hotel sauna in the city, wrapped in the most considered hotel in the city, you've found it. Book the spa time when you reserve the room; this is not a wander-down-in-a-robe situation.