This is a neat combination of seeing Mayan ruins and bird watching while sailing on a lagoon. You will find the angels at the entrance to the tomb of the Ek' Balam king (and nowhere else!). Afterwards drive straight up north to Río Lagartos. See the map for distances and the time schedule. Find more details in my relevant posts, just click the links.
Ek' Balam (Ruins)
It's an offbeat site compared with nearby Chichén Itzá and you will have it to yourself. The startling stucco sculptures on the entrance of the king's tomb in the Acropolis will really impress you; they represent the local king's journey after his death, down into the underworld (Xibalbá) and then up to the heavens via the Tree of Life. You can climb the Acropolis (160m high), which is not allowed by now at all Mayan sites.
Equip yourself with some interpretation of those Angels. It will help you understand their story when you stand in front of them.
Río Lagartos (Hammocks/lakes)
You will drive to the village of Río Lagartos. You can have lunch here at the restaurant Ría Maya or Villa de Pescadores, both on the waterfront, and take a boat from there to sail through the lagoon Ría Lagartos for 2 hours, to observe pink flamingos and even have a float in the truly pink lagoon at Las Coloradas point (ask for this specifically when you get on board).