39 pesos (about $2 U.S.); free (ages 0-11). There is an additional 40-peso fee to access the boardwalk down to the lagoon, and a 50-peso fee to enter the Sian Ka'an Biosphere Reserve. Rates for the 1-hour boat cruise are negotiable and average about $25 (U.S.). Cash only.
Daily 8-5. Allow 1 hour minimum.