Big hotels dominate the best stretches of beach. All of Mexico's beaches are public property, so you can use the beach of any hotel by walking through the lobby or directly onto the sand. Be especially careful on beaches fronting the open Caribbean, where the undertow can be quite strong. By contrast, the waters of Mujeres Bay (Bahía de Mujeres), at the north end of the island, are usually calm and ideal for swimming. Get to know Cancún's water-safety pennant system, and be sure to check the flag at any beach or hotel before entering the water. Here's how it goes:

White Excellent

Green Normal conditions (safe)

Yellow Changeable, uncertain (use caution)

Black or red Unsafe; use the swimming pool instead!

In the Caribbean, storms can arrive and conditions can change from safe to unsafe in a matter of minutes, so be alert: If you see dark clouds heading your way, make for the shore and wait until the storm passes.

Playa Tortuga (Turtle Beach), Playa Langosta (Lobster Beach), Playa Linda (Pretty Beach), and Playa Las Perlas (Beach of the Pearls) are some of the public beaches. At most beaches, you can rent a sailboard and take lessons, ride a parasail, or partake in a variety of watersports. There's a small but beautiful portion of public beach on Playa Caracol, by the Xcaret Terminal. It faces the calm waters of Bahía de Mujeres and, for that reason, is preferable to those facing the Caribbean.