Definitely do Doc's Cave. We have been there three times. When you get off the ship just catch one of the taxis (buses) and tell them to take you to Doc's - it costs 3 or 4 dollars each. You will pass Margaritaville along the way. It costs 3 or 4 dollars each to get on the beach. It is clean and they have things available to rent. I suggest an umbrella. They have snorkel stuff - but it's not the good stuff. When you're done frying just head back up the street - it's just a short walk to Margaritaville. Grab something to eat and go back to the ship or back to Doc's - just make sure to get your hand stamped before you leave Doc's. You can get a water taxi or regular taxi back to the ship.