Card catalogs. (There is nothing cooler. Except perhaps for the books themselves.) They are the memory banks of the library…in a really big one, like the Library of Congress or the NY Public Library, they are like the library’s brain. You can literally look inside the library’s brain to find the location of the book you want. But in the process, you might find out about many other interesting books. In comparison, looking up your book on a computer screen is like phone sex as opposed to real sex; like a gray cloud as opposed to a rainbow; like skim milk as opposed to a chocolate sundae. Card catalogs were GREAT.