The most striking building in Mayapán is the round observatory tower. The Maya were talented astronomers. They were especially obsessed with the movement of Venus and other planets, as they believed these were gods traveling back and forth from the Earth to the underworld and celestial planes. The round tower is built on a foundation that was divided into two semicircular zones. During the city's heyday, these rooms were covered with plaster and painted. Visiting the archaeological excavations of Mayapán, one cannot help but think of the similarities with Chichén Itzá and the Kukulcán pyramid, the Temple of Venus, and the observatory.

Although its shape is compared to the Chichén Itzá observatory, it does not resemble an observatory as such, mainly due to the lack of windows for conducting measurements, insufficient height for observations above the trees, and because it is located in an area with a high concentration of buildings. Since the upper part of the building has been lost, it is unclear whether it was built of stone or wood; the observatory could have been located there, but there is no evidence of this. What is likely, however, is that it was used as an astronomical calendar because it has points indicating the sunrise and sunset positions, which were used as calendar markers.

The round temple has four entrances and was built around 1350. Polychrome wall painting remains were found inside; the colors and design of the mural suggest a direct connection with the frescoes in the Hall of Frescoes. It appears that the building was painted in Maya blue on the outside, a color used only for the elite. The building has an approximate diameter of 10.2 meters and a height of 7.5 meters and was constructed on a rectangular foundation measuring 20 meters long, 18 meters wide, and 3.5 meters high. Its walls are 1.15 meters thick, and inside there is a cylindrical wall with a diameter of 4.5 meters featuring several niches at the bottom. The temple also has two small attached structures, which represent an altar on the foundation and a sanctuary.

Sources:

https://mayanpeninsula.com/sitio-arqueologico-de-mayapan/