Usually when you go to a library, everything in the collection is easily accessible and in plain view. That includes books and audiovisual materials that you may check out. It also includes computers, magazines, newspapers, reference materials, etc. that you must used in the library. But what treasures lie behind a locked door marked “special collections”? It’s mostly academic libraries that have a special collections department. If they’re very old, then some of their earliest acquisitions have become both old and rare. They’re rare because most other libraries have “weeded” those items out of their collections long ago. After all, as new materials come in to a library, they have to get rid of old things that no one uses any more.