This non profit organisation offers various organised trips into the biosphere, numbers are limited to no more than 12 people per day and tour.
There's a an all day tour and a sunset tour as well as kayak, fishing and turtle -watching trips. We went on the sunset tour, which included pick up at our hotel in Tulum, a swim in a cenote, an explanatory talk by our guide at the centre, a guided walk through the jungle, a boat trip on the lagoon to Boca Paila and a bird island, water, fruit and a deliscious dinner back at the centre.
Very recommendable.
Address:
Tulum Sian Ka'an Biosphere Reserve Quintana Roo Mexico