WARNING: ON WEEKENDS, DAY PASS USE OF THE SPA IS NOT AVAILABLE, EVEN TO HOTEL GUESTS.
The Cosmopolitan heavily promotes its spa/hammam as a key reason to stay there, however it's not available if you stay there on weekends. I tried to buy a day pass for the hotel's spa on Saturday, but was refused entry, even though I was a guest of the hotel.
Although it is a policy that does not appear anywhere on the hotel's website or in-room services directory, no one can use the spa on Saturdays unless they also purchase a very expensive treatment...and some of those have starting prices of $300.
I'd never heard of a hotel banning its own guests from its spa, especially when they advertise their spa as a key feature (it was one of the reasons I booked this hotel), so I complained. The response was to offer me a marginal discount on one of those $300 treatments! So to use the steam and sauna we had to leave The Cosmopolitan and schlep to another hotel spa on the strip, which was happy to welcome us and sell us a day pass.