Unfortunately I was using the Poison Room _only_ as a reference point. I have been through it and I know about the hidden room immediately along its southern wall. I am talking about another possibly large hidden room area on this same level and other hidden rooms in general and how a character detects them. Maybe the answer is that one needs to walk into the walls to find points where you pass through into a new hidden region?? Is that how you do it or is there a skill to develop?? I can't find any skill mention of detect hidden doors or the like.
Thank you.