If you have a car and are willing to trek to maryland, there’s a great place on Georgia Avenue just south of the beltway. They specialize in wedding dress preservation and have a few options ranging from just cleaning to packaging it in a nice windowed box.
Don’t just take it to the most convient place. You should make sure you take the dress to a place that regularly deals with formal wear. You would hate to have the dress ruined by a botched attempt to get a cake stain out.