Equinox Hudson Yards
While a number of Equinox clubs have spas within their fitness centers, the Hudson Yards location in New York City practically has a spa within a spa. This location's fitness center has a wide array of fitness equipment, group fitness classes, dry and steam saunas, four pools (including a rooftop pool), and an outdoor lounging area with complimentary towels.
Equinox's actual spa (run by Equinox Hotel) has a list of varying hair, face, and body treatments for needs ranging from scalp treatments to sports massages. Did I mention there's also a dry sauna in that section of the fitness club?