I've done two spa days in my life and both were awesome.
The first was a massage, facial and feet at The Spa at the Mirage. It was $65 or so and lasted an hour. A hot woman massaged my neck, arms, hands, and feet then put on this cream and heated mitts and booties. While this was happening she gave me a Rose Water facial. I left there feeling awesome! This was the only massage in Vegas which didn't end with me getting a happy ending.
Second was a complete day at Camelback Spa in Scottsdale, AZ. Went for the $185 Gentleman's Day and it included a mud wrap, Swedish shower, deep tissue massage, neck and head massage and facial, healthy lunch, and private pool. Again it really leaves you refreshed....