people answer a bunch of questions to obtain the coordinates for a library computer which they then go to, and there they do a few more calculations to determine the dewey decimal number of a book
We are currently working with one of our local libraries to place a cache there. Their rules, however, will not allow us to put an entry in the library computer for the cache, since it is not an actual book that can be loaned. We visited another cache in a nearby library whose coordinates led to the library door and the title of the cache was simply a string of numbers (which, of course, turned out to be the Dewey Decimal number assigned to the book/cache). It was only a blank journal-type log and was placed in the maps section of the library. You could also place it in "hobbies" or really a number of other places in the library and let your clues lead cachers there.
One suggestion: we also have done a "book/box," but found that most geocaching books in print are fairly thin. You need a substantial, hard-back TOME to make a good traditional cache. We ended up buying a big medical book from the library when they were cleaning house and used that-- along with a fake book jacket that we created. Note: make your book jacket first and put it on the book (including a plastic cover from the library) BEFORE you start creating the book/box. Once the pages are glued together and the center hollowed out, you will have a hard time adding the jacket.