It is the best known building on the site. Since its discovery in the last decades of the eighteenth century, it has attracted attention for the quality and aesthetics of its architecture. It has 365 niches, which gives it a symbolic value associated with the solar calendar. It was built during the last phase of development of the settlement. This structure is remarkable for the differential finishes of its decoration in several construction periods. During one of them, high quality stucco moldings were included, representing small columns crowned by elements in the form of segments, as well as inverted pyramids. In other periods, magnificent mural paintings illustrating mythological characters were painted with very fine strokes of mineral pigments.