Carlo, If you are going to Capri on your own (there is no reason to pay extra dollars to Carnival) you simply walk off the pier in Naples, make a left turn, and in 2 minutes you will be at the ferry terminal (the same place that Carnival uses for their tours). Simply buy a ticket on the next hydrofoil/jetboat to Capri (there are several different companies with boats,,but they are all pretty much the same) and after a 45 minute boat ride you will land on Capri in the small town of Marina Grande. As you start to walk off the ferry pier you will see signs on your left (still on the pier) for the boats to the Blue Grotto. You buy your boat ticket and get on the next boat which will take you around the island of Capri to the entrance of the Blue Grotto. There, you will pay another fee to a man in a boat, and than you will be transferred from your boat to another much smaller row boat that will take you into the Blue Grotto. They will row around for a few minutes, sing a song, and than you reverse the entire process to return to Marina Grande. This is going to cost you about $35, it is one of the great tourist traps on earth, but its something everyone does once! From Marina Grande you can also get the funicular up to the town of Capri. If you are on your own, I would suggest you buy your return ticket to Naples before you leave the pier to explore Capri...thus avoiding any lines when you are ready to return in the afternoon.