If you think that a beach can't get much more beautiful or romantic than Cancun, then hop on a boat and take a trip across the water to one of Cancun's outer islands. Isla Mujeres is a good choice. Though no longer the best-kept secret it once was, Isla Mujeres remains cleaner, chiller, and less crowded than Cancun. Just five miles long and a half mile across, the island is flat and is ringed by beaches. If you're looking for islands that are more remote and calmer still, try Isla Contoy, a wildlife and nature reserve, or Isla Holbox, both of which are north of Isla Mujeres.