miles away , pass invisibly across something that is itself invisible , but which buzzes like a swarm of flies as it drags itself over the ground ... continue , the roads and towns and trees rushing behind you with zip-zip noises , until you come to the big city and , near the centre of the city , the high old tower , and beneath the tower the ancient magical university , and in the university the library , and in the library the bookshelves , and ... the journey has hardly begun .