The single best thing I did on the 7-day cruise was snuba with my son, in St. Thomas. Thank you so much to the wonderful woman on this board who posted that information and then corresponded with me about it.
This is not a Disney-offered excursion, and it is only for swimmers who are interested in the diving experience. I
was interested because we are divers who have a son who was getting to experience his first underwater experience. If you are interested, I'll describe it. If you are not, please skip over this post.
You need to be at least 8 years old and in good health. You can be a grandparent. You do NOT have to be a certified diver to do snuba. You essentially go diving, but you are limited to 20 feet depth (hence no decompression worries) because instead of carrying the air tank on your back, the tank floats in a narrow inflatable raft on the surface, and it moves with you as you go, but you don't really notice the movement. You breathe through a regulator, just like "real divers", so you have to get comfortable doing that, and you do descend up to 20 feet, so you do have to learn to equalize, which means every so often in descent you simply pinch your nose shut through the mask and blow so your ears pop (pop is too strong a word). That equalizes the pressure.
You wear all the same equipment "real" divers do -- mask, snorkel (actually in snuba they tell you a snorkel is optional, but I would alway recommend a snorkel while in the water, you never know what might happen!), fins, regulator and hose, but the tank floats on the surface above you, and weight belt. Make sure you get enough weight!
The instructor spends some time in shallow water with you standing up experimenting with your gear, while they "teach" you some things about what you'll need to know. My personal opinion is that those things take some practice to be able to do -- like really clearing your mask underwater -- the kinds of things you learn in the process of getting certified -- so I recommend this event for adults who are enthusiastic snorkelers and decent swimmers and who are interested in the diving experience, and not claustrophobic or afraid of new experiences, PLUS the children who are old enough and good enough swimmers and who want to do it.
As I mentioned, it was the single best thing I did on the cruise. I also took some underwater photos I will treasure for a long time.
I would heartily recomment this event. Remember, you have to do it on your own!