I took my mom to the Waldorf Astoria spa for manis and pedis on her birthday in October. On my own, I would have done massages and facials, but I wanted us to spend time together, so this seemed better. My mom had never been to a place like that and was totally floored by the experience.
Anyway, the spa had a good ambience. It was of course $$$$, but that's no surprise. I was bummed, though, that the pool and hot tubs were all outside and co-ed. I.e., they just gave you access to the hotel pool and hot tub. My other experience with a super-posh spa was at Caesar's Palace in Las Vegas, and there they had multiple hot tubs, cold tubs, steam rooms, even a snow room ... all gender segregated, so you could, er, choose to wear as much or as little as you might want. That was also the case at the less-glamorous Imperial Palace, so I kind of thought any high-end spa would be like that. Maybe it's just a Las Vegas thing? (I hate casinos, but they sure have nice spas!)