Stock Photo: Sunset seen from the Sian Ka´an Biosphere Reserve, in Riviera Maya, Mexico, which is a small ecotourism and education center, it serves as a model for sustainable development in sensitive tropical ecosystems It is a UNICEF World Heritage Site and is the. Sunset seen from the Sian Ka´an Biosphere Reserve, in Riviera Maya, Mexico, which is a small ecotourism and education center, it serves as a model for sustainable development in sensitive tropical ecosystems It is a UNICEF World Heritage Site