Washington D.C. Suggestions

Check out a show at the Kennedy Center. You can also take nighttime tour of the monuments
Make sure you visit Arlington national cemetery, eastern market on a weekend morning, newseum. Caps games are fun!
Fine dining: Rasika, Proof, Jaleo, BlackSalt
Casual dining: Graffiato, 2 Amy's
Bars: Poste, POV lounge

Definitely see the monuments/memorials at night. It'll feel more relaxed and personal when it's less crowded. The Korean War memorial is better at night due to the effect of lighting and shadows.

I also agree with rooftop dining at the W, overlooking the Whitehouse.

Also go old school with a meal at nearby Old Ebbitt Grill. If you've only experienced gulf oysters, get their oyster sampler for varieties you may have never had a chance to try in Louisiana.

Take an Uber to the Washington Hilton to visit the location where Reagan was shot.

Rent kayaks in Georgetown to take in the views along the Potomac.

Rent bikes to explore the DC area more efficiently. There are also bike trails in the Arlington area that will take you to Teddy Roosevelt island. Bikes and vehicles are not allowed on the island, so you'll have to use a bike rack and walk across a foot bridge, but this worthwhile destination is usually not very crowded. It gives you a glimpse of what the DC area looked like prior to it becoming the nation's capital. You'll be close enough to continue to Gravelly Point where you can experience large commercial jets flying right above your head.

For people watching, have lunch in the cafeteria of the Hart Senate Office building. Also try happy hour at one of the Union Station bars, but sit in the area where you can be seated in the Union Station lobby area.

Take one afternoon to go up and down King Street in Alexandria. It's a historic areas that was frequented by our founding fathers. The Metro Blue Line near your hotel will take you there.

Don't leave without going to the Pentagon. The inside may not be a big deal, but visiting the memorial area where the plane hit on 9/11 makes it a worthwhile visit.

Smith Point, Town Hall, Mason Inn