I agree with Greg on diving the Kittiwake. But also diving with the sting rays would be fun for all problem is they are on opposite side of the island for that. The wife & I were able to dive about 12 of the west coast side (which is where the Kittiwake) is resting and we had a blast.
Remember the Grand Cayman Island prides itself on having 365 dive sites (1 for each day). The reefs range from approx. 40 feet to over 100 feet and are full of live.