After a 28 year hiatus, I have weirdly found myself travelling to our nation's capital twice in the past six months. To be fair, that 8th grade class trip really wiped me out. The Smithsonian is so big.
I barely knew anything about the place before, except that Washington D.C. is filled with trinkets and expensive monuments meant to make me proud to be an American (and something about terrible public schools and mayors who do drugs), but I'll tell you what I have really come to appreciate: the public transportation system. The WMATA seriously kills it, and clearly other proud Americans think so, too. That's why you can easily find this handy guide to staying at hotels near train stations (and you can fast forward to the map to compare to your hotels.com searches if you're saving up those free room points). In fact, you can easily visit all the patriotic stuff (I joke, it really is some breathtaking stuff) on the Metro, tour many of the area's colleges (which is how I was able to string together a whole recital tour without ever renting a car), and plan your meals based on Metro stops.
If you are planning a trip to D.C., I implore you to take advantage of all of the amazing public transportation available to you. It's convenient, easy, and driving in that town is totally stressful if you're not familiar with the crazy street system. In my off hours during my last visit, I jumped on and off trains and tried to cram in as much national culture as I could.
Triple B Fresh, a Korean deli in DuPont Circle
Hirshhorn Museum and Sculpture Garden, L'Enfant Plaza
Kennedy Center for the Performing Arts, Foggy Bottom Station
Clyde's of Gallery Place
Nando's Peri-Peri in Chinatown