Uh... Last time I checked my History, Neither the Mayans nor the Aztecs inhabited Peru..
It was The INCAS!! 
...And.. Aliens?!?!?!
Why must History be twisted so?! 
Thoughts? Don't try it with this movie.

This is one movie that the more you think about it the more it falls apart. In the moment, first time watching it's OK, after a few viewings it's flaws really come out, I'll probalby only watch it again with the Rifftrax. Even Temple of Doom with the crazy magic stones holds up better than this one.
We've got:
Selective magnetism.
Mass X acceleration of a lead lined fridge being tossed several miles and landing = boneless Indy
Did the Roswell and other aliens come back to life when the one alien got it's head back? And how did he/she/it lose it in the first place if it was held on with such strong "magnetism"? What was the deal with them all merging and getting their skin back? Why did they need to "lift off" just to wink into another dimension? The entire alien plot line is turned into a mess by the way they did the ending.
So many more, could go on for a long time.
One more thought: They should have made Dr. Irina more evil during the movie, did they ever show her actually killing anyone? Her fate at the end seemed a bit excessive for what she actually did during the movie.