What is the name of the tour you are going on??? If this is the place I think it is and the way to get there is a road across the highway from Mismaloya, it is beautiful. We were there many years ago, but I do not remember what they called it.
As I recall, it was cooler at that place than it was in town. PVR is in the tropics and will probably be hot and humid when you are there. Take whatever you would take with you to the beach (ocean or lake) - there will be sun and swimming, but also shade if you want it.