At the back of the Observatory is the Hall of the Mascarons of the god Chaac (the rain god), which can also be seen in other Maya archaeological sites. Additionally, the temple has a series of columns that once supported the roof. The Hall of the Mascarons (Mascarón (from the Italian mascherone — large mask) is a decorative element in the form of a mask of an animal, mythical creature, or mythological character, placed in architecture) of the god Chaac is a platform that closely resembles those found in Uxmal and, primarily, in Kabah. There is a possibility that they were moved from Kabah due to their complete similarity to the mascarons in the Kotz Pop temple. It is also possible that the inhabitants of Mayapán visited Kabah and copied them or hired builders from there.

It has a grand staircase, an altar, and columns dividing its interior space, which in turn supported the roof. Besides the masks of the god Chaac, items such as an altar can also be found. Because of the mascarons, it is believed that the frieze was also decorated with Puuc style elements, since this type of mascaron originated there. Inside the hall, there are two benches attached to the walls and a sanctuary on the central wall. The roof of this structure was flat, supported by walls, columns, and pilasters, consisting of beams and mortar. Apparently, the function of this building was related to ritual activities and religious ceremonies.