The Library of Congress

 If you are local, for the love of all that is holy, go and get yourself a library card at the Library of Congress (yes, you can!) and spend as much time as possible wandering. It’s amazing. I don’t know how to do it justice. If you’re not local, this is another one of those things that is completely worth a tour, but if you’re strapped for time at least wait in line to pop inside and see the reading room.