Snorkeling with whale sharks, the world’s largest fish, is an experience you won’t soon forget. These gentle giants congregate in large numbers along the northeastern tip of the Yucatán Peninsula from around mid-May to mid-September and typically measure 6–7.5 meters (20–25 feet) and weigh more than 10 tons. (They’re known to grow upwards of 18 meters, or nearly 60 feet, though such behemoths are rare here.)

From Isla Mujeres, whale shark tours leave around 7 a.m. for a 60-to-90-minute boat ride northwest past Isla Contoy toward Isla Holbox (where such tours first became popular). Once in the feeding grounds, you’ll see the huge sharks trolling along the surface, feeding on krill. The boat is maneuvered nearby the shark, and a guide plus two guests slip overboard and swim alongside.

The big fellas are surprisingly fast, despite their languid appearance, but kicking hard, you’ll have a minute or so to admire their gaping mouths and sleek spotted bodies. The smaller your group, the more chances you’ll have to get into the water, though most people welcome the short breathers between turns. Rules also require that boats not linger with any one shark more than 30 minutes, so you’ll get up and close and personal with several sharks during the tour.

Most of the tour operators and dive shops listed in this section also offer whale shark tours, charging US$95–125 pp, including gear, guide, light lunch, and drinks.