We will be spending 9 days at TTR end of March/ April. Besides the Boobs Cruise is the any excursion that you would recommend. According to previous threads Isla Mujeres seems very popular and we might check that out while there. Would prefer not to spend half the day on a tour bus also.
Last year we did a day trip to climb coba, swim in a cenote and visit a traditional mayan village. It was pretty awesome esp as they are closing down climbing of most of the ruins
We went to Chichen Itza, and swan in a Cenote with the tour company at TTR. Went in a 12 person van and had beers all day, it was a great time! The drive is a little long, but with a beer in hand, it's not bad. It's cool to see some of the local culture too.
"xplore" was awesome. ATV driving, zip lining, lazy river through caves. Also day trip to island was awesome as well, rent a golf cart and drive around the island.
If you like snorkeling Xelha is a cool place to go. Swimming with dolphins is available. Cliff jumping (not real high though) is there as well as tubing. Full day though, unless you do a half day and split it with Tukum.
Another vote for Isla Mujeres. Tulum is fascinating, and only 60-90 minute drive from TTR. A great trip is to tour there in the morning and stop in Akumal on the way back to snorkel with the sea turtles. You can rent the equipment and grab lunch right there on the beach.