To anyone out on spring break right now: I went on a cruise to the Caribbean recently. If you're the type who wants to go SCUBA diving, but aren't certified, there is SNUBA. Same thing as SCUBA, but instead of wearing an airtank on your back, it floats in a raft and you're tethered to it with an air supply hose. Somehow this isn't regulated (yet) and anyone can do it. The 10 minute safety video and then away you go with your guides is kinda sketchy, but if you're confident you can keep your anxiety in check 30' underwater, without any prior training, its an awesome experience!