My honest first question when I read this is: Isn't knowing about every single passage and doorway absolutely critical to security in a facility where high risk persons work? It seems absolutely crazy to me to think that, as a US comparison, they would let the President go anywhere that might have passages the Secret Service is unaware of.
The doorway only leads to a small empty room. The actual passageway was blocked already in previous renovations, so there was no danger of anyone coming through it.
Even as an internal only room, could someone hide in there?