From the introduction:
The Library - Well, it goes on forever. I'm not kidding here: it really does. You have no idea how huge this place is. No idea. There may have once been something outside of it, but it was just built around all that stuff. That said, it's not just bookshelves: look hard enough you can find forests, lakes, swamps, even full mountain ranges and oceans in here, and some other interesting biomes as well (ever been in an purprose quagmire? You don't want to). Of course, these have all been turned into some sort of book-storage, from carved shelves on vertical cliff sides to rickety reading rooms on stilts above the waves. The library is dotted with villages, towns, even entire cities and whole civilizations within its infinite borders.
At the center of the Library is the Catalog, and the office of the Head Librarian. This massive structure serves as the hub for the groups of adventuring Readers, as well as the centralized location of all discovered books in the Library. There's still more to catalog.