This is a wonderful place to visit -- you don't want to miss X-Caret!
It is an eco-park where you will find a lot of fauna. The nice thing about this place is the many underground rivers, which are totally safe even for little children (with parents). You pay for your ticket and you have access to most of the activities there. They have snorkeling and something called snuba, which is like diving, but you breathe through a hose and you go walking under the sea. They have bat caves and a very brief play at night about Mexican history -- you must watch it! They have little plays and pre-Hispanic dances all around the park, plus a horse show of the charrería mexicana. You will find a tulip park and the beach there is beautiful. The underground rivers are so cool -- they provide you with a life jacket and you swim along the river. They have several entries and exits and it is not deep at all plus there is no way of getting lost in there. They have raccoons, birds, a butterfly sanctuary, and a little museum for children about how butterflies live.
It is a huge park so it would be recommended if you are traveling with your family to bring radios to communicate to each other so everyone can enjoy what they want. A great place to visit!