This unusual structure is one of two once very similar structures that flank the stairway leading up to the main northern building at the Nunnery. Its frieze presents some common Puuc motifs, including geometric mosaicwork, angled upper and lower cornices, and deity masks at the corners. Access to its inner chambers is through a very wide space, although the large span is divided into five doorways by means of four columns with geometric carvings that visually lighten their volume and make them more appealing through the play of light and shadow.