Heading for Cozumel next month on RCCL. We've done Chankanaab etc. and are considering renting a car and visiting the "national" park on the southern tip of the island. I think it's called Punta del Sur. There is supposed to be a lighthouse and some birdwatching available. Has anyone been before? Is it at least as good as Chankanaab? Any snorkeling available? Thanks for any info!!