Structure B-X3 is a step pyramid with sides so steep that it is almost cubic in shape. This temple platform would originally have supported a perishable superstructure but no trace of this now remains. The pyramid faces west and was accessed by an extremely steep stairway with fifteen steps that faces directly onto the massive high retaining wall of Group B. The stairway is flanked by wide balustrades that form the western facade of the temple platform. Structure B-X3 has been restored.