Walkthrough for the "Tribes of the East" expansion.

4th campaign, 2nd mission – I can’t figure out how to complete it after 3 days. (I move the city, defeat everyone, and go into the dungeon, but I always reach a dead end. I’ve found all the obelisks. The map has some kind of path; I run along it, and there’s a crystal and a head, and in the middle, something that looks like a crystal, but I can’t take it. What should I do? Please provide more detailed instructions. Thank you in advance.)