Mexico: Isla Holbox, Cabo Pulmo and Bahia de los Angeles

A shark the size of a whale might sound like a science-fiction nightmare, but whale sharks (Rhincodon typus), which are three times the size of the biggest great white shark, are peaceable creatures unperturbed by visits from curious humans. Mexico's Isla Holbox, possibly the best place to swim with the world's largest fish, recently hosted the International Whale Shark Conference, during which the country's National Commission of Natural Protected Areas (known by its Spanish acronym CONANP) declared Aug. 30 International Whale Shark Day.

Whale-like only in size, whale sharks are in fact sharks, but they're dolphin-like in their sanguine and playful personalities. They swim around at a leisurely pace, sucking in thousands of gallons of water to filter out microscopic plankton, krill and algae. The greatest danger to humans is getting too close to one of their cavernous mouths (opening 5 feet wide) and getting gulped in with the plankton. (The shark will obligingly and promptly spit you out, but it's not likely to be a pleasant experience.)

Snorkeling or diving with these giant fish is a unique and awe-inspiring experience, and this is Mexico's peak season. Though they typically stick to the deep waters of the ocean sea, Mexico is blessed with several locations where whale sharks frequently surface close to shore

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