We went to the Sian Ka'an from the south. What is cool about the south entrance is that there is nothing but beach on one side and Mangroves and lagoons on the other. There aren't any hotels in the south end of the biosphere, but we stayed at mayan beach garden - www.mayanbeachgarden.com - and they made us some maps and packed us a sack lunch. They even gave us a shovel if we got stuck. We didn't, thank goodness, but we experienced one of the most beautiful beaches I've ever seen in my life. The beaches were varied too. We also snorkeled to a sunken ship. in every case, we were the only ones around. In one way, it was kind of unnerving to be the only humans there, in other ways it was the most spiritual experience I've been through. We went after Dean and there were no entry fees. According to the owners of Mayan Beach Garden the fees used to be $20 pesos a person, but the entrance was damaged by the hurricane and hasn't been restored (march 2008). We never made it all the way to Punta Herrera because we kept stopping along the way to explore the beaches. We were told that the town of Punta Herrera is one of the most secluded and last fishing villages of its kind with one restaurant and a little tienda. we were glad for the packed lunch because our explorations took up all of the day. We did see a group of peccaries (not sure of the spelling) crossing the road - they are like javelinas.