So much golden knowledge and opportunity to glimpse into a civilization with real antiquity were lost/destroyed during the Spanish blitz... I sincerely hope that something that offers some more clues is found down there.

Do you know why it was sealed and if, for sure, nobody has been down there since?

If they find a Neanderthal in there, I'm gonna crap my pants!

Whoa! This is the first time that I have seen in print from a legit source that it was built by someone other than the native people." The place where men became gods." Very interesting.My gut tells me that we will not hear about this anymore once the cave is open.Wonder what made them seal it back up.The fact that it was built over a cave is very interesting as well.

There is a plethora of possibilities as to what this tunnel could be. Remember that the actual builders of the city of Teotihuacan are still debated although it is often associated with the Aztec civilization. The tunnel could possibly have some sort of astronomical measurement purpose as is often found with civilizations of this caliber. For example, the Great Pyramids have shafts through the stone from the inside to the outer walls that seem to serve no purpose at all except for the fact that they may have lined up with the Orion Constellation nearly 10,000 years ago (obviously this is far older than the age of the pyramids as they are dated today--entirely different mystery).

Could this tunnel serve a similar purpose?

I'd recommend reading Fingerprints of the Gods when it come to a subject like this. It is very interesting but not always convincing. Draw your own opinions!