I was on the Zuiderdam this past summer, the Hydro Therapy Pool and Thermal Suite are 2 different options, the total for the 2 for the week was $125.00 per person. They are key card access only and are located right off the Lido Pool.
However, when looking at the deck plans it doesn't look like the Rotterdam has those facilities - however, i could be wrong.
Grand Princess 12/05
HAL Zuiderdam 07/05
Caribbean Princess 08/04