Of course, Cancún is all about the beach. Still, no trip to the Yucatan peninsula is complete without a trip to the historic Chichen Itza, the most famous city left behind by the mysterious Mayan civilization. But once you're done with the ruins, get on a cruise and relax on the blue Caribbean Sea and perhaps even go snorkeling. If you want to go swimming somewhere more unusual, head to Xcaret and go swimming in an underground river!