You can never forget how close you are to history when you walk along the waterfront in Old Town Alexandria. Just take a look over your left shoulder, and the US Capitol looms on the horizon. Walk along the brick sidewalks, and take a gander at townhouses that are as old as our country, and provided a roof over some of the nations founding fathers' heads.
If the history doesn't get you, watching the sailing boats pass you by might tickle your fancy. I quite enjoy walking past the docks wishing that I could have this boat or that one, despite the icky-ness of the water that is the Potomac River. There are iron benches to sit on and watch the boats sail by, or watch the planes land overhead at National Airport.
During the summer, street performers stake out there own corner of the waterfront and entertain the passers-by with hopes of a donation. Balloon-animal-making clowns, tap dancers, musicians -- you name it, you'll see it. Be generous, most are pretty good.
In the evening, it's quite the romantic spot. A popular place in May and June for the prom-goers, all decked out in their finest. There's also a rather romantic restaurant on the pier, the Charthouse I believe.