Sian Ka'an (translated of the Mayan it is "Where the sky" or "Gift is born of the sky") is located 24 km south of Tulúm, Sian Ka'an, which means "where the sky is born" in ancient Maya, was decreed a nature reserve on January 20, 1986; with additions made in 1994 and 1998, it currently stretches over a total area of 650,000 hectares –10% of the state of Quintana Roo.

The reserve encompasses all the main ecosystems in the Central America and the Caribbean and its flora boasts 800 classified vegetable species. A total of 2,161 different animal species have been registered to date, including 339 types of birds, 103 mammal types. Reptiles in the area include the green, loggerhead and hawksbill sea turtles.

Its coast boasts 120 km of coral-reef barrier, which belongs to the second most important reef system in the world, the Great Mayan Reef. The fresh, clear waters offer an unparalleled coral formations 84 types of coral, more than 450 fish species and countless other life forms.

Within the boundaries of the Sian Ka'an Biosphere Reserve is Bocapaila on a 20-meter-wide peninsula, which then stretches for another 25 km towards Punta Allen at Ascension Bay.

There are five entrances to the reserve, located in Pulticub, Santa Teresa, Chumpon, Chunyaxche and Chac Mool. Guard parks, working by governmental organization SEMARNAT, are in each one of the entrances to make sure the fulfillment of the regulations within the reserve.