Celestun is in Yucatan.
Celestun is a small village on the atlantic coast of Yucatan an hour drive west of Merida. Its main tourist attraction is the Celestun wild life reserve, a feeding and breeding place of the flamingo. Most tourist visit Celestun as a daytrip to see the flamingo's and have a seafood lunch.
Travel to Celestun with the oriente bus driving from Merida Noreste bus terminal. There are also collectivos from Celestun to Merida. Collectivos leave from Calle 67 between 50 and 48 between 10am and 3pm on the hour. Price is similar to bus fare.
Celestún is famous for their Mangroves and, especially, their Flamingos! You can book a tour from Mérida or you take a bus to Celestún and get a tour there. At the beach there are many boats that sell you a 2-hours-tour for 300 MXN (March 2019). However, almost 1,5 hours of that tour consists of getting into the mangroves and out again and the boat guys don't stop for any other animal than the Flamingos. On the entrence of Celestún there are many boats waiting for passangers directly inside the mangroves. You might get a better deal there! Just hop off the bus at the entrance to town after crossing the bridge (or when you see the boats on the left side).