The long peninsula of Baja California separates the Sea of Cortez from the vast Pacific Ocean, creating an undersea treasure that the whimsy of nature has turned into a three-ring underwater circus. Jacques Cousteau called this sea "the biggest aquarium on earth." In savvy dive circles it has become known as "the fish trap of the Pacific." It's a world of unforgettable experiences. One morning you'll spot a commotion on the water and spend two hours cavorting with a school-bus-sized whale shark; then, in transit to the next dive site, you'll be surrounded by hundreds of dolphins; and in the afternoon you'll never want to stop playing with endlessly curious sea lions at isolated islets. Whole trips can be spent off the many uninhabited islands of Los Islotes where California sea lions congregate in great numbers. As long as you feel like staying in the water, they'll zip and dash and interact as if the sheer act of satisfying their curiosity fulfills their every need.

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There are even wrecks: Near Espíritu Santo and the Cerralvo Islands you'll find the Salvatierra, the Lapas 03 and the Fang Ming, which attract vast fish shoals — grunts, snappers and creolefish — which in turn bring in hungry pelagics. On the rocky substrate there are corals as well as pink, orange and purple gorgonians, and among this colorful ornamentation are jewel and zebra morays, puffers, surgeonfish, parrotfish, frogfish, soldierfish, angelfish, hawkfish and stingrays — just a sampling of the variety of species that coexist here. One of the most thrilling experiences to be found is an encounter with the compact groups of mobula rays, often numbering in the hundreds and blotting out the sun as they pass overhead; sometimes you'll even see them jump out of the water in great, Olympic leaps. Other big creatures such as mantas, orcas and a wide variety of whale species are more seasonal, but you always have to be alert and keep an eye to the water -- any movement or irregularity in the sea surface may signal a surprise in the Sea of Cortez. In deep contrast to the fertile sea, the desert landscape topside seems endless and, with the exception of saguaro cactus, scrubby shrubs and withered trees, devoid of life. The reality is much different, but on first glance it seems as if all life in this place fell into the sea.