Try snorkeling around the TMM dock in the sea grass on the North side, plenty of seahorses there.

Cancun is not the kind of place I would normally go, I'm more of a backs woods off the beaten path kind of guy but in this case it's just a means to get to our main destination. I'll probably try Playa and Cozumel next year and I'd love to stay in the old section of Merida as well.