I have written a little bit about my experiences in Cancun, and if you are so inclined, you can read about it here: http://justaskjudy.blogspot.com/2005/05/happy-cinco-de-mayo.html
Once on the Isla Mujeres, we donned our snorkels and masks and were led out into a channel. About 20-30 yards off-shore, we spread out over the reef to see the fish. This was my first time with a snorkel, so I didn't venture below the surface. Actually, I have a very hard time getting underwater, as I am not a strong swimmer and I float so well. There were probably 8-10 different types of fish to see, and it was interesting, even from the surface. After that adventure, we dressed for the picnic, or what passed as a Mexican version of one. In an open air buffet/cafeteria line, we were offered many different types of Mexican foods. My stomach was tenuous at best, so I played it safe with the offerings. My son was in HEAVEN! He ate some of everything, but then he has a cast iron stomach, while mine is made of hardware cloth.
We sat down on redwood picnic tables, and were soon joined by macaws and other birds, looking to filch a morsel of something. My son, who has always been good with animals of all kinds, had the macaw on his shoulder in no time. Later on, the monkeys appeared, and true to form, he had one of them sitting on the crook of his arm in short time. The monkey was loving the bits of watermelon he was given.
Some people wanted to swim with loggerhead turtles, who were in a fenced-in-area specifically set aside for this. The swimmers were warned not to try and ride on the backs of the turtles, because they whip around to try and fling you off. Of course, you know what happened. There's always an idiot in the crowd. One guy (about 25 years old) just had to cling to the back of a turtle, who showed his displeasure by veering back and forth in a rather violent manner. At one point, the man's foot grazed a nail that was sticking out of a fence rail underwater, and when he emerged from the water, he was dripping a huge trail of blood. No one had any sympathy for his, as he had blatantly disregarded the warnings by the tour guides. They bandaged his foot as well as they could (they were not prepared for this) and we boarded the catamaran for the trip back to Cancun Beach. I don't know what happened to the guy, but he did have to go to a hospital for stitches. I am thankful to this day that I didn't let my son swim with the turtles, else he might have been the one with the slashed foot.
Maybe soon, I will tell you about the fiasco in the airport that preceded this trip to Mexico. It's a long one.