After many years I've learned the trails that lead through the rooms of the second floor that ignore the offices filled with desks and metal file cabinets that are filled with paper and plastic discs. These are private places owned by the workers in the library and I do not invade them.
The doors that serve as passage are solid wood with cold brass knob and handles. They are closed and locked at night except for the halls and storerooms and through these I pass in my nocturnal musings.