How do I get into the City

Hint 1 of 6:

Have you recued Aiela yet?  You'll need something she has.

Hint 2 of 6:

Talk to Oaxtepac in the Tichticatl jail.  Ask about the great gem.

Hint 3 of 6:

Find the secret door just soutwest of the teleport plate complex.

Hint 4 of 6:

You will need to wake up Yunapotli to get through the door.

Hint 5 of 6:

He is missing his head, and his brain.

Hint 6 of 6:

You'll find his head in the palace, the brain with Fritz.