I am going on A Princess cruise on Aug. 12 and I have the tour book in front of me
There is a place, X-Caret Eco-Archeological Park, which has snorkeling, swimming the blue lagoons, snorkel the underground rivers, lie on the beach, walk through the botinical gardens plus other activities. The place offers horseback riding and "dolphin encounters". Never been there but its an option for you. I know the other place, Chankanaab, is good-I've been there.