In Grand Cayman there is a tour that takes you to swim with stingrays (Stingray City, I think they call it). There are many...many stingrays that swim all around you. You swim with fins and goggles. I thought it was one of the most interesting tours there.
Been there done that. 3 feet of water and hundreds of those things all around you. "Shuffle your feet on the sand and don't step on one" was the rule.