This OUTSTANDING aviation museum is an extension of the Smithsonian National Air & Space Museum, located on the property of Dulles Airport. Free admission but pay to park. Great if you're bringing kids along.
There are DOZENS of gorgeous places to have an adult beverage (most also welcome children and pets) in Northern Virginia. We have a few we like a lot, including Stone Tower Winery, and Walsh Family Wine, which are in or close to Leesburg. There are also many breweries in the Dulles area, including Old Ox, Solace, and Aslin.
One Loudoun is a mixed-use center located pretty close to Lansdowne Resort. There are many casual dining spots there, plus a movie-theater, Barnes & Noble, and other shops. Top Golf is located pretty much across the street (but don't try to walk there).