Thanks for feedback.
Serene 56- Yes we are on an RCI cruise also- after looking into the land and sea we found the boat trip is in a semi-submarine that stays on the surface and the Atlantis goes under almost 100'. I think we will chose the Atlantis.
Chiquita- thanks for the tip-will probably do the Submarine- still deciding on which port...
Tim T and My2cents- thanks for the honest feedback on the trip. We have seen other posts about Grand Cayman and figure we will try the submarine there. We have read/heard that Stingray City is really crowded and can be somewhat dangerous with the crowds. I guess we are just chicken!