The Persian Garden has 3 "rooms" (a sauna, a meduim heat steam room and a turkish bath) and 2 scented showers. It has a heated bench to relax on between using the other rooms and an ice machine. I think they charge $20 per day or $100 for the entire cruise. If you get another spa treatment, you get the use of the room for that day.
We signed up for the entire cruise and went there every day at about 6pm. It was quite with half of the ship at dinner.