Which airline and airport? I said St. Louis, which has a direct flight from IAD on United on a commuter jet that I've been on long ago. We didn't fly directly to St. Louis when we took our kids.
If the credit is with United, I'd look at their flight map and see what interests you. Other airlines may have something similar.
https://www.united.com/en/us/destination-map
We've also flown direct to Nashville for a long weekend (3 nights), took a cab to a downtown hotel (got there before lunch) and didn't rent a car. We took the hop on/hop off bus one day and walked the others, but we like to walk. Nashville tour and museum entry fees add up, though.
Also did similar with San Antonio. You can bike or Uber to the missions from the River Walk, but we walked everywhere else. Even with the time change and longer flight, it was a great 3-night trip. It helps going that direction that you still arrive in the morning even with a 3.5-hour direct flight. So I wouldn't rule out going a bit further if there's somewhere that interests you that gets you there by lunchtime.