I've just reached an elevator in the bandits barracks, at the base of the battle tower. Sassan said me to find Erlking the (mute) goblin and name of the demon.
I have the same problem. I'm on the second floor at the base of the battle tower, and i got a key from the creature who wakes up from the torture table. The map seems to show a hidden room behind a chest, but i can't get to it. What am i supposed to do?