The Pyramid of the Sun was a location in the ruins of Teotihuacan, Mexico. Azerim had fled their with his machine part and became a ruler of the Olmec civilization, using their help to guard his machine part. The Pyramid had several ceiling mounted doors rigged to open by using three animal- shaped keys: jaguar, fish, bird. Azerim had the roofs closed to keep out the sun that shone very brightly in the pyramid.
During his quest for the machine part, Indiana Jones arrived at the pyramid and began to explore it. While dodging its various booby traps, Indy reopened the ceiling doors and aquired a reflective mirror for a statue at the lowest level. Unfortunately, Russian Spetznaz troops led by Dr. Volodnikov appeared to hinder his quest. While dealing with them, Indy put the mirror on the statue and the light reflected off of it and opened a massive door that led to an unmapped valley of the Olmec.
The mirror also served Indy in a much more perilious adventure as he revisited the pyramid from the Aetherium and used the mirror as a weapon against Marduk to reflect his lightning attacks.