This was a challeneg entry a long time back. If you look at the shelves on the left of the pic the "back" mirror is mid shelf. The gap between the shelving units is where the the fron of the shelves repeats in the reflections. I did the hallway then composited in the man and desk which was a second render where the back mirror was replaced with a simple 2d plane. I'll post those in a second reply.