spaceIn Somerset, England, there is a very old and very famous cathedral, which is home to a very old and very famous library. Less famous, however, is the second library housed on the grounds, deep below the lower levels. Built simultaneously with Wells Library, the United Kingdom Library of Wizarding History and Literature (as it was dubbed in the early 20th century) can only be accessed via the floo network, thanks to a special fireplace enchanted to be invisible to muggles, and hidden rather out of sight besides. There is a small pot of floo powder on the fireplace's mantel, which magical folk may use to whisk themselves down into the magical library.
spaceLike the Wells library above, it houses a large chained collection of books that cannot be removed from the premises. They are, in fact, cursed, so that should one successfully break the chains holding the books, they shall remain rooted in the spot until a library attendant releases them (and replaces the book). However, there is also a large lending library, and the pages most books can be duplicated with a Gemino charm (though the books as a whole cannot be, and any book that contains information on dark magic cannot be duplicated. The library has windows which are enchanted to mimic the view outside the windows of the upper library. It is quite easy to get lost in the library, so it's always recommended that you pay attention to where you're going. Magic is not permitted within the library, except in the form of enchanted note-taking quills.
