This structure has the most beautiful frieze in Chichen Itza, with a vast number of masks of the god Chaac on the sides. All the facades of the Annex are decorated, in keeping with the Chenes style.
The principal façade has a frieze displaying masks of Chaac in either side of a central medallion above the entrance. Set onto this is a sculpted figure in stucco, with a head-dress of beautiful feather and fret patterns.