Building 17, called the Twin Pyramids, is located on the west side of the South Plaza and represents the best-preserved architectural ensemble. It is a large foundation on which two or more platforms were built, and on them, two vaulted buildings with four rooms each were constructed. The structure measures 40 meters in length, 17 meters in width, and about 6 meters in height. Beneath the building we can now admire, there are two structures that were completely hidden: ancient Maya architects used buildings from earlier eras as foundations for constructing new buildings.

The inscriptions on the painted vault allowed for precise dating of the construction, making them a very valuable find in the study of architecture. An interesting and unusual fact is that the ceilings were made from logs, traces of which are still visible in the lime mortar. The facade decoration of the buildings in Ek' Balam was not done using figures carved into stones, as in Uxmal and Chichen Itza, but with plaster or lime mortar shaped in various forms and then painted. The building preserves remnants of stucco painted red, suggesting that the facades could also have been that color. Considering that the structure partially collapsed, especially at the front, it is possible that the decoration on the back, left exposed, was completely destroyed over time, although it might have been stolen. Other decorative elements found exclusively in this building are stone cornices located at the outer corners of the rooms, which is unusual since they are inside.

The exterior decoration of these buildings was stucco and limited to wide friezes; on later walls, we can still see pedestals where sculptures once stood. Small fragments of stucco and two anthropomorphic masks have been preserved; this was the only example of decorative stucco found here. Traces of paintings in black were discovered on the walls of one of the rooms, consisting of very rough geometric and zoomorphic figures.

These drawings apparently appeared after the construction and may have even been made after it was abandoned, as the crude technique indicates they were done by people without the skills seen in other samples found during archaeological excavations.

Beneath the building we can now admire, there are two structures that were completely covered: ancient Maya architects used buildings from earlier eras as foundations for constructing new buildings.