There are so many, so see which peak your interest. (Address if for National History Museum which is in the middle of most of them)
The Newseum is CLOSING at the end of 2019! if you haven't gone yet, it's multiple floors of history told through the news and newspapers, so do try to go.
The best bakery! Get the chocolate chip cookie dough cupcake
If you're in town early, check out the boathouses! They run along the river (Key Bridge in Georgetown, near the monuments at the Tidal Basin, the Wharf, National's Stadium). You can rent a variety of fun water boats, like kayaks, stand up battle boards, and the foot-paddle boats that look like swans. Specifically, the tidal basin location will allow you to view monuments while you paddle.
Yummy pizza and sangria (which is on the Happy Hour menu too!)
This is a great cocktail lounge below Ambar. Drop in and grab a cocktail and sit in the plush, velvet chairs.
Our second home, and the best sushi