
Xel-Ha is an ecological water park, where an inlet creates a natural aquarium, and you can snorkel, swim, float down a lazy river through the jungle on an innertube, swim through a partly underground river, or even just relax on the beach. (You can "SNUBA" here, too, but that's a whole other story!) We had a lot of fun here, even though we were only here for half a day. (We did the combination tour of Tulum and Xel-Ha when we stayed in Cancun a few years back.)
I learned to snorkel here, and I think it's my favorite snorkeling experience still. Since it's a natural inlet, there are no waves, and you can swim to the shore anytime you want (it's surrounding you on three sides.) Very relaxing, very stress-free. (No fearing of being left behind like in that freaky Dark Water shark movie!)
Swimming in the underground river was pretty neat, and the innertube ride was an activity for everyone to enjoy (just be sure to wear the really strong sunscreen!) 
This is one of the places where you can swim with the dolphins (these places are popping up all over the Riviera/Cancun area) if you're interested. It does cost a pretty peso to get up close and personal with the dolphins, but some people just love it. (I've always had to pass on this one.):) You can find more info on their site.
Check out the XEL-HA MAIN WEBSITE for more detailed info on all of these fun things to do!
