I now make it a point to schedule an Athlete's Recovery 80 minute massage on every trip to Vegas. It's a combination of deep massage + intense stretching. Both times have been with LaQuisha who is incredible.
Booking a massage also grants you all-day access to the spa which is very nice. Multiple hot tubs, a cold soak, sauna and eucalyptus steam room. The co-ed pool is a great place to unwind for a bit post-massage.
Would have been five stars if not for a completely baffling and infuriating design/layout choice. The outdoor co-ed pool overlooks Liquid, Aria's "day club" pool, which begins blasting loud music at 11am, completely killing the zen vibe. So if you want to enjoy the pool, best to do it first thing in the morning.