I think I can help you! Traveled to the Yucatan many times. Found out the BEST way to enjoy two wonderful excursions in one. First: Rent a car/jeep. Tulum and Xel-Ha (Shell-ha), are a short drive from Cancun or Cozulal/Playa del Carmen. Plan to arrive at Xel-Ha as early in the am as possible. (All the tour busses arrive at noon). If you arrive at 9 or 10 AM, you will have the entire magnificent lagoon to yourselves. Then, about noon, drive to Tulum for a 1-2 hour tour. Then you can "Beach-hop" up the coast, (Take any right turn to the sea) You'll find quiet beaches, pina-coladas, palm trees, and alot of serenity. I almost moved there in 1990 to run small tours myself. E-mail for more details.