Tour the Sian Ka‘an Biosphere Reserve. My tour began with a boat ride through the biosphere. We were dropped off in a channel that the Mayans used for commerce for a floating expedition: it took a little getting used to! We sat in our life jackets and strapped them on, so we would be able to float along with the current. There were fish in the channel, mangrove tangle along both sides. We saw birds, butterflies, etc. The freaky part was that you would almost expect a snake or crocodile to come out!
After this adventure, we got back in the van and went to the nearby Muyil ruins. They are not completely excavated, and nowhere near as big as the Tulum ruins, but beautiful just the same. After all of this, we went to a nearby cenote for snorkeling and swimming. The water was not as clear because of earlier rains the area had had, but there were many fish, and the water was refreshingly cool. An excellent adventure!