Washington DC is our home, so we have tons of suggestions and will slowly be updating this page. For now, here’s our Walking Tour Map.
Our Self-Guided Walking Tour Map:
The Monuments are really neat to see at night. The Lincoln and Jefferson memorials are really well lit and the glow takes awesome pictures. Also, there’s something really neat about the Korean memorial at night. The darkness makes you think about and appreciate everything that the troops did. 
Plus, it’s not as hot and there’s much fewer crowds. We highly recommend it.
Here’s our map that involves 100% walking & public transportation. It hits the following: Smithsonian Metro, Jefferson Memorial, Franklin Roosevelt Memorial, Martin Luther King, Jr. Memorial, WWII Memorial, Korean War Memorial, Lincoln Memorial, Vietnam War Memorial, and ends at Foggy Bottom (just keep walking straight North from my map a couple more blocks), all with the Washington Monument in the center of your tour. A total of 3.8 miles, but it’s very flat and there are nice, even sidewalks the entire route.
Hope you find our travel guide helpful!