There are two choices. You can take a tour there, over an hour boat ride on a catamaran, on the island activities like horse back riding, boogie board, banana ride, etc. and lunch. Go through King David which is one of the best. Or go to the passengers terminal building and take a taxi to the pier to stone island which is next to where the Mexican Navy is based. It is a 5 to 10 minute ride by taxi (about 5 to 6 us dollars per cab) There are these small boats that run every 10 minutes to stone island and should charge at the most 20 pesos (2 dollars) If you donīt know the area I would recommend you take the tour and next time do it on your own. But it is your decision of course. If you are interested in a tour of the city, that is what I do. Have a great time!