The Waldorf-Astoria Guerlain Spa (CLOSED)

This impressive 14,000-square-foot spa manages to be a serene oasis despite its opulent decor, which includes silver ceramic-tiled walls, white marble floors and a floor-to-ceiling glistening crystal chandelier at the entrance. The treatment rooms are the size of most New York studio apartments (complete with private bathroom, shower, locker and vanity area), making a customized Guerlain therapy the ultimate indulgence.