I'm also stuck on this quest. I checked the walkthrough and apparently there is a door to be unlocked. I believe I have found this door (left side of the room just before the big room with the blue crystal object). However, I can't interact with the door. I can click the ground on the other side as if there was no door, and my party attempts to go there, but the door is obviously in the way. I have a "heavy iron key" in my stash, and I can't take it out of my stash for whatever reason. I assume that is the key I need? Help needed asap please, been playing this game non-stop since I got it earlier today and would really not like it if I had to stop playing due to a bug in a critical point of the story