I walked along the National Mall past the National Gallery and Smithsonian Museums. I had been to them on my trip last November so didn't revisit them again even though at that time they weren't open.
The Washington Monument is at the end of the National Mall. The Monument was damaged by an earthquake that occurred in 2011 which I actually felt when I was in NY. It is known as the Virginian Earthquake.
Last time I was in DC the reflecting pool was being repaired and was empty so I was rather excited to see it had been fixed and reopened. The reflection with the National Monument is really amazing.
The Lincoln Memorial was were Martin Luther King Jnr gave his famous I have a Dream speech. The Lincoln memorial features a museum below the statue that details event surrounding that speech.
From there I walked up past the infamous Watergate Complex from Richard Nixon's presidency to the White House. In this light it doesn't look that white but at night it is extremely white. Previously I had seen Secret Service forces on the roof.