If you are traveling in the area, don't miss out on all of the amazing cenotes that dot the region.
I usually rent a car and drive down the highway towards Tulum and stop at small signs that says "cenote."
Many are on privately owned property like the one above, and cost about 40 pesos for entrance. Some of the most popular are: Cenote Azul (Blue Cenote) near Playa del Carmen, Gran Cenote in Tulum, and also Calavera near Gran Cenote.
On the road between Tulum and Coba are many smaller ones.
If you are really adventurous then head about 2 hours the other direction from Cancun to Valladolid and check out the one in town, and the 2 on the outskirts.
I would avoid all of the big, touristy ones like Dos Ojos and others that are adventure parks. Not as much fun and they cost a lot more.