We visited the Dos Ojos cenote as part of our tour with Edventures, I assume you can also visit on your own if you wish to snorkel and it looks like there are organized scuba dives.
Dos Ojos is located in between Playa Del Carmen and Tulum, it's one of the longest underwater cave systems in the world. Dos Ojos is Spanish for two eyes for the two neighboring cenotes. We just snorkeled, our guide took us into the bat cave for which you'd want to have some sort of flashlight to avoid knocking your head on the stalagtites and also to be able to see anything at all.
We didn't see many fish, this is fresh water, not salt water and you visit the cenote to see the rock formations, not the fish. The water is cool, most people had on at least a 1/2 wet suit but after being in the water for a minute I was fine with the temperature.
The area between Playa del Carmen and Tulum has some of the best cave/cavern diving in the world. Everyone should experience a "cenote" while visiting the Riviera Maya. If you are not a diver, I recommend a swim or a snorkle. Try Armando Elizalde of Scubacenote $85 USD for a double tank dive (lunch and equipment included). Best deal around and an excellent tour with an excellent guide.
i took one of the cenote tours close to playa del carmen (mayan zip-line, riviera may). i thought it was worth the time and money. don't expect a lot of lingering for wildlife viewing, but definitely a way to see the cenote's and see how the mayan culture permeates the yucatan.
Cenotes outside of Playa called Aktun Chen. It's a hour long tour. A little pricey (no credit cards), but it was a great tour. Our guide was terrific and went back and forth from English to Spanish for the people on the tour.
The dirt road from the highway to Aktun Chen is about 5km so take a car or taxi. My husband and I made the mistake of taking a Collectivo!!
Take a break for the tropical sun and head for the forrest to explore the vast network of underground caves called "cenotes". These caves are occupied by bats, lagoons and Mayan relics. Go with a guide so that you don't end up lost forever in this maze of caverns.
The little helmets are not a fashion statement. I thought something this small could never protect your head, NOR did I think I would actually run into a stelagmite...wrong on both counts. They worked like a charm. Necessary and provided on the tour.
South of Playa Del Carmen you will find endless signs for Cenotes. We didnt have enough time for all of them, so we chose one that combined the cenote with a small wild animal park.
The Cave was spectacular!