THere are many options in grand Cayman...Ride horses on the beach, snorkel, diving, rent wave runnes, rent a boat...charter a sailboat, atlatis submarines etc...have a look at Cayman Islands Discounts Guide for info on what to do in Grand cayman and how to save money doing it. Enjoy
Don't do the Atlantis submarine! It dives in deeper water where the light doesn't reach really well. Everything looks blue - like in a swimming pool. You couldn't see the pretty colors of coral, and unless a fish swims up close to the sub, everything is just varing shades or the blue - sort of like a black and whicte TV, only shades on blue instead of gray.