Pat, the cenotes I'm aware of are south of Playa del Carmen just north of Tulum. There are several of them, however I don't know how many are available to the public, due to possible dangers. I think there are a couple where you can enter by paying a small entry fee. When I went to Dos Ojos (or something like that, means two eyes in Spanish) it was with a dive group. We also had snorkelers with us. The scuba diving is unbelievable as you work your way though the caverns. The snorkeling was just OK at this site because you could not go very far on the surface. If I remember correctly, the big amusement type park in that area ( Xarcet ?sp) has a cenote the visiters can float thru on innertubes. It was something I'll never forget.
Fins up!!! Marty