If you haven't spent much time in Washington, DC, we strongly recommend taking a day to explore the city and check out the many free landmarks around. These include the various government buildings, monuments and memorials, and the Smithsonian museums. These are popular with tourists, but are in no way "tourist traps." They're sites that have legitimate cultural and historical significance. (Just plan on bringing food, not buying it there, or you will have to pay tourist trap prices!) One major caveat, however, is that the 25th anniversary of 9/11 is the weekend of the wedding. To our knowledge, no plans have been announced for any major protests or memorials for the event, but there's a decent chance something will be later. Double check your plans before you go, and consider having a backup just in case.
This mall is within walking distance of the hotel block. The shopping is so-so, but the restaurant selection is fantastic! Nando's (attached to the mall) and Silver Diner (in the parking lot) are particular favorites. Those with dietary restrictions, take note: Silver Diner is one of the most vegan-friendly, allergy-friendly restaurants around! There's also a Target where you can pick up anything you might've forgotten at home, and a Dave and Buster's for the gamers.
The local park. Go for a run on the trails, say hello to the ducks, or rent a canoe. The perfect place to spend a low-key afternoon.
A local pizza place right down the road from the venue, with a full bar. We're regulars at Thursday Night Pub Trivia.