There's not much to do at Watergate except look at it, at least right now. There is supposed to be a Foggy Bottom Trail in progress but the signs aren't up yet. I'd recommend doing that trail when it opens, hopefully later this year.
We went to the Lincoln Memorial to talk about the March on Washington, of course, and also Marian Anderson's concert on its steps in 1939 when the Daughters of the American Revolution wouldn't allow her to sing in Constitution Hall.
Hughes Mews and Snows Court are some of the only places left in DC where you can still see how the old alleys and interiors of the city blocks were used for housing. Definitely worth a stop.