...never forget!
You see, there weren't any more books. There was an underground road.
When I say "road", I mean it was wider than your typical hallway. One of those oversized golf cart style urban rubbish collector cars would have fit through.
And in fact, there sitting next to the door were rubbish bags. I'm pretty sure that was the whole point of this passage, to allow for easy garbage disposal without obstructing the traffic outside and littering the streets.
But looking up and...
5/n