Oh, I totally want to do this one. I've been tubing down regular rivers, but I've never tubed through a cave!
For the "tubing" novices, this is the fine art of flopping your backside into an inner tube and doing nothing but socializing with other tubers and taking in the scenery while the current carries you downstream. If you're looking for a rigorous physically challenging shore excursion, this one isn't for you, but if you're on vacation to relax, tubing is a perfect way to do it.
(Hey, you can always hit the treadmill in the gym when you get back onboard the cruise ship.)
Here are some details on the Belize cave tubing excursion:
"Located about 33 miles on the Western Highway are some of Belize most popular caves and experience of a lifetime. After a 6 mile off road drive into the rainforest, we will arrive at the fabulous Cave's Branch of the Sibun River .
After briefing by your guides, and an exploratory walk through the broadleaf rainforest you splash into the cool water of the Sibun River aboard your inner tube, caving light on your forehead, and float lazily downstream for an hour and a half.
Enjoy the cave formations of this Cretaceous Period limestone cavern, formed by the Sibun River , long before the dawn of humankind." (from Kelly Tours)
I love caves, so this one goes on my list of shore excursions I must take someday.