I highly recommend skipping anything in Cozumel that requires the ferry, especially during the winter months. Somewhere on these boards (can't find it without the search) I posted a review of our miserable trip to Tulum. The ruins were cool, but not worth the pain of travel, particularly the ferry crossing which is notoriously difficult. We're doing another Western in January, and I definitely will be staying on Cozumel island. We'll use the mainland stop at Costa Maya to see some ruins.