A bad library is a mess. Children's fiction mixed in with the cookbooks, art history stacked on top of engineering manuals. No books seem to leave the building, because nobody can find what they're looking for.

A good library is a haven of organisation. Every book has its place, and if one is moved, the librarian will make sure it gets home again. It is a hub for readers, who walk in and out with stacks of books, taking them home to enjoy.

But the best libraries are inherently unordered, because there is no filing system that can impart structure on the wonders they contain. Books of mystery and magic, alchemy and sigaldry, a million million worlds waiting to be explored. And it is vanishingly rare for any to be taken away - because how could you waste time leaving, when you have a book like that in your hands?