The most important structure within the archaeological site of Teotihuacan is undoubtedly the imposing Pyramid of the Sun (La Pirámide del Sol).
On one side and approximately in the center of the Avenue of the Dead, stands this ancient pr-Hispanic building nearly 63 meters tall.
An interesting but unknown fact to visitors, is that under this giant pyramid is a tunnel that leads to a room located right in the center of the structure.
It contains four small irregular caverns that possibly had some religious purpose in ancient times. Unfortunately there is no public access to this corridor but now one can see a small metal door attached to the front of the structure.