Park Hyatt New York

Spa Nalai sits on the 25th floor of the Park Hyatt, and its party trick is a pool wired with underwater speakers piping live audio from Carnegie Hall next door — which tells you exactly how seriously this place takes its quiet luxuries. The dry sauna and steam room are part of the same calm, light-filled floor, all pale stone and considered hush. The hotel itself is a model of understated Midtown polish: large rooms, deep bathtubs, the kind of service that's present without hovering. It's not flashy and it doesn't need to be. For a heat session that feels genuinely restorative rather than scene-y, with one of the most civilised hotel pools in the city attached, it's hard to beat. Sauna and pool access is included for guests; just check the spa's daily hours when you arrive.