With all due respect to Norm's opinion......man that crap he recommended is all BORING! And besides you will spend all day traveling to the mainland to do the Tulum and eco park. I made the mistake of doing Tulem while on my honeymoon in Cancun. If you want to see the "rocks" rent the movie "against all odds" from @1985 it was filmed in cozumel and had one scene where sexy Rachel Ward takes the ferry over to Tulum to draw pictures. The eco park does sound ok but it seems to me to be the kind of place you would go to if you were staying the whole week and wanted to kill a day off the beach and out of the bars. Stick to the water while in Cozumel. Snorkle / scuba and party on the beach!