There are many great displays at the library—such as one of the original Gutenberg Bibles—but I think people often forget that it’s still a working library. In fact, it is the world’s largest library. It has more than 160 million items!
Time permitting, I always recommend friends plan to research something while they’re at the library. This way you can take advantage of the opportunity go onto the floor of the main reading room (that’s the famous round room featured in National Treasure), which is the only way you can see the architecture at the top of the dome.
Before you go, be sure to check out the short-term displays back at the Jefferson Building. They’re always interesting and available to the public whether you have a researchers card or not. Even if you don’t have time to do everything I’ve written about here, I’m confident you won’t regret taking time to stop by the library. If nothing else, you’ll see architecture you won’t forget and some memorable photos!