Cruise ship spas typically have not only treatment rooms but also saunas, steam rooms, and thermal relaxation suites. Most lines waive the access fee if you book a treatment — which is why it's surprising when you get a $200 massage and don’t get access to the facilities. On Royal Princess and Regal Princess, for example, you should be prepared to pay about $50 more for spa access.
The Solution: If you're not getting a treatment, but want to use the thermal suite, booking a multi-day pass may be the best deal. In addition, Viking Ocean Cruises doesn't charge any fees for passengers who what to use the saunas and steam rooms — whether you're getting a massage or not.