Everytime we visit Playa del Carmen, we set aside a day to visit Xelha (shell-ha), an ecovogical park about half hour south of Playa del Carmen.
You can get there by bus from Playa del Carmen if you don't have a car. Entrance fee is about $30 - $50 if you want the all-inclusive food and beverage plan. We never seem to have enough time to want to spend it eating and drinking.
Lockers and rental snorkeling equipment are available (tote yours along if you can - it's pricey). Life vests and floating tubes are complimentary.
Restaurants and bars are scattered throughout the park - strolling musicians provide entertainment - lounge chairs are everywhere under palm trees to shade you from the hot sun.
Snorkeling is incredible, especially near the floating bridge - ask when they are going to feed the fish and make sure that you're there (the biggest fish I have ever seen - almost scary but I just had to get in there with them). This is not to be missed.
There's a flowing river that goes through caverns, ropes that you can swing on to jump into a pool, caves that you can snorkel in - can you tell that I'm excited?
There is a train that takes you through part of the park. They safeguard your belongings until you appear at the other end.
For the less adventuresome there are teak lounge chairs, massages, an aviary, or the beach (a little corally) for quiet relaxation.
This park is less "touristy" than Xcaret - that's what we like about it. Try it once - I'll bet you'll be hooked! Let me know.