[SPOILER] Brennenburg Castle's overall layout (complete map)

[cantremember]

Like you said, I don't think they had an overall castle layout, but worked on rooms individually, as some areas overlap (guest room and study being the easiest to spot), in the archive tunnels there are two different corridors and doors that lead to the same spot in back hall, and according to your map, the back hall is facing a different direction compared to entrance hall, and is actually in front of the main entrance gate (you'd expect it to be at the back of the castle, and the stairs facing the same direction as entrance hall I think)