We took the boat trip from Alexandria, Va to Georgetown. It was so wonderful! You see a lot of the DC area landmarks & monuments plus go under several bridges. Then you can walk around Georgetown and either ride the boat or take the Metro back. My kids loved seeing the other boats and kayaks on the water and seeing the airplanes overhead that land at Reagan. Well worth it!
Another way of seeing Alexandria that is easier on your feet than walking is to take this forty-minute narrated cruise that reveals history, legends, and a view of Catain’s Row, where sea captains once lived. The company also offers a narrated boat tour of Washington landmarks, passing the Lincoln and Jefferson Memorials and the Washington Monument and turning around in Georgetown Harbor.