You are correct, there is a pressure plate to remove a wall (if you could get through the busted door near the start of the dungeon, it is the wall to the right that is fake; you can remove it from the other side if you follow the passage around to the end). If you run the crosshairs along the apparently decorative rock/brick strip about 3 or 4 feet of the floor on that wall, you should find the pressure plate.
