In front of the main temple, on the platform where the stairs are raised, there is a small rectangular altar, also added in the last constructive stage. In three of its sides it has embedded sculptures of skulls and quadrets with the representation of crossed bones. The researcher Alfonso Caso described this altar as the tomb of the solar god. In the interior there was a painting with the same motifs, whose remains were removed to stop the deterioration. However, in the site museum of the archaeological zone, called Xólotl, a reproduction of that painting can be seen today.

Wall of the pyramid where the Altar of the Skulls can be seen