Downtown Leesburg is a great visit to either stop and get a bite to eat, pop in an antique shop, or a small boutique. The address listed here is for Lightfoot Restaurant, which was renovated into a restaurant from an old bank, but will take you to the heart of downtown.
If you feel like going out a bit further for a hike check out Sugarloaf Mountain. It's a local favorite and It can be a great half-day activity. Hiking from bottom to top is about an hour and if you feel like getting to the top just for a view you can drive most of the way up as well.
One of our favorite dates was a hike at Sugarloaf and then lunch at Sugarloaf winery just down the street. They offer some snacks but if you want to save some money we recommend picking up a lunch on your way in or eating before hand.
Another great downtown option that isn't as big as going to DC. Frederick is bigger than downtown Leesburg with more shopping and dining options. September is still Crab season for us so make sure to stop at Avery's for some crabs if you aren't venturing down to the water at Annapolis.