Short DC visit (Washington, D.C.)

I am attending a meeting at the NIH from Wed to Fri, 4pm of this week. I have Friday night and Saturday morning -lunch in DC before I leave for Chicago (airport by 4pm).
I have visited the many wonderful museums and monuments in DC so I am after a different side of DC. That is the local side of DC. What do you recommend for a very short DC stay?

Anna