You'll go up to Cabo Catoche, the closest place to mainland. Some people say that this was the first place where the Spanish arrived when the were dicovering America. During the trip you may be fortunate enough to spot some dolphins while they swim around the boat.
Once you arrive at Cabo Catoche you can snorkel and see a little reef, home of nursehsarks, starfishes, coral and different kind of fish. You will also have some time to fish and eat a fresh ceviche on board.