Most of Cancun's activities involve water-related fun in the great outdoors. Among the many things to do are snorkeling at a unique underwater sculpture museum; swimming with enormous whales sharks off the coast of Isla Contoy; ocean and cenote diving; birdwatching and hiking on an uninhabited island; and boat tours through mangroves.
Diving & Snorkeling
For decent snorkeling you need to travel to one of the nearby reefs. Several dive shops now offer diving and snorkeling outings to Museo Subacuático de Arte (MUSA), a unique underwater attraction designed to take pressure off nearby natural reefs.
Most of the major resorts rent kayaks and the usual water toys; a few make them available to guests free of charge.
Cancún has pretty weak surf, but a core group of locals still head out to Playa Chac-Mool and Playa Marlin to hit the little rollers. ‘Surf season’ runs from October to March. There’s no place in town to rent boards, but there's a downtown surf shop where you can buy one.