As others indicate, you do not have to stay or have a room booked. They do have day passes for the water park, we were there recently and checked on that... the ropes course, game room, magi quest... and pretty much everything available can be paid for individually.
Not at all you start early an make a day of it. Just come prepared to ruff it a bit
I believe now you can buy day passes for the waterpark.. but I would call them to double check
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