Where do you park

I didn't park. I used the metro but as stated in other comments if you use a garage expext to pay up to $20.

I went on a Sunday. I parked on the street. The metered parking was cheaper to me than parking in a lot and you have the option to pay your meter online if you dont think you will make it back so you dont have to keep going back and forth. All I did was get the meter number and website off the meter, signed up and added the extra time I needed. I found parking right near the museum.

There are lots of paid parking lots in the vicinity. Or outside the city and Uber in.

I parked approximately 5 blocks away in a secured parking lot. Unfortunately I can't remember the name of the lot, but I parked there all day and it was only $20. I do remember the parking lot being down the street from a Starbucks and a 5 minute walk to the museum.

There's plenty of metered street parking by the National Mall. But i suggest parking outside the city and taking the metro in. Cheaper and easier than circling around for street parking.