3355 Las Vegas Blvd. S.
Las Vegas, NV 89109
The largest spa and fitness center facility in Vegas with over 130,000 square feet of treatment rooms, workout centers, salon, aerobic studios, a café, sauna, "environment rooms" (steam, rain, cold, etc.), and even a rock climbing wall.
It's one of the more expensive spa facilities on The Strip but there is so much to do (and have done to you) that you get a lot of bang for your buck.
Because you want to get a massage, take a pilates class, have a spa lunch, get a facial, and then climb a rock wall all without leaving the facility.
The spa is open to guest of the hotels and the general public. Book a treatment and you get a discount on using the fitness center and spa facilities.
Bigger may not necessarily mean better, but it does mean more options, which is always a good thing.