I just got back from the western Caribbean on the Paradise (Jan.11)
We sailed to Belize, although the weather was rainy, we went cave tubing with Reggie. It was marvelous...a definite have to do!!
You first take a van for about 45 mins, then hike through a jungle(rainforest) Then you hop on a tube and float through a stream and rapids in caves with a headlamp...very cool!!
If you look up Reggie's cave tubing, send him an email and reserve a spot...I guarantee it will be cheaper($65) than booking it on the ship, and you will be at the same place as the people who do book it and pay the $85-$100 on the ship.
Best of luck, and enjoy!!