The Zona Arqueológica comprises the excavated areas around the incredible Pirámide Tepanapa and the tunnels underneath. You enter via the tunnel on the north side, which takes you on a spooky route through the center of the pyramid. Several pyramids were built on top of each other during various reconstructions, and over 8km of tunnels have been dug beneath the pyramid by archaeologists to penetrate each stage. From the access tunnel, a few hundred meters long, you can see earlier layers of the building. You don’t need a guide to follow the tunnel through to the structures on the pyramid’s south and west sides, but since nothing is labeled, they can be helpful in pointing out and explaining various features.