General Discussion

I was born in Washington DC 1950. I would recommend seeing the National Zoo in Rock Creek Park, free I thinks, beware parking fee was $25 last I went couple years back, an all day metro pass might be better, tho nearby road parking is free if you can find a space, and read parking warnings carefully.
Then I would suggest the National Art Gallery, free, cross the mall from the smithsonian museum. Recommend seeing Thomas Cole painting done 1840 'the voyage of life', you can preview it, link below, I hope. Art Gallery frequently hosts a known painters actual paintings on loan, if you go let me know who this time. I saw Cezanne once.
https://en.m.wikipedia.org/wiki/The_Voyage_of_Life

Then I would suggest seeing the African American museum, free, near the Art Gallery, but this requires a reservation made in advance so visit or call, unless there is a military veteran with you, they should allow all members in his/her party in immediately without reservation, no pun intended.
The Af Am museum's bottom floor configures a ships below decks where slaves would be kept as they voyaged from Africa. Interesting and informative 4 or 5 stories. Fairly new.
Georgetown also interesting.
I used to just ride the metro to different lines limits and back for a quick tour. You see a lot of inner city with much different aspect from the refined mall. Hate to say it, but best not to debark in some places, especially after dark.