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My daughter and her husband were recently on the Carnival Triumph and they did do the Tulum excursion and booked it thru Carnival. It was a long day...I think it says it's approximately 7 hrs. long for this excursion but I could be off a bit. They were in Cozumel the entire day and the ship did not leave until late evening so they had time for this. I have also done this excursion from Cozumel when we were on a Royal Caribbean cruise years ago. We took a ferry ride (about 45 min or so) to Playa del Carmen and from there took a bus ride over to Tulum (this was at least an hour if memory serves me right). As others have said this is not an excursion I would recommend booking on your own. The beach there is beautiful and the ruins were interesting.