What room in both houses was out of bounds at all times the boy in the striped pajamas?

In "The Boy in the Striped Pajamas," the room that was out of bounds at all times for both houses was the room at the end of the narrow corridor at Bruno's house, where the family's maid, Pavel, would clean. It was forbidden for Bruno and his sister to enter that room by their parents. At the concentration camp, the room that was off-limits at all times was the commandant's office.