Bikers should check out the Mount Vernon Trail.  This 18 mile trail runs south from Roosevelt Island, through downtown Alexandria along the Potomac River, and continues to George Washington's historic estate.  The trail is paved, so it is suitable for road bikes, and it is mostly flat with only a few difficult hils and sharp turns.  Of course, hikers can enjoy this trail as well, as long as they are prepared to share it with a lot of bikers.

The Washington & Old Dominion Trail is another great choice. This trail begins in Alexandria and follows the old tracks of the historic Washington and Old Dominion Railroad, heading 45 miles west to Purcellville.   It is paved, making it suitable for bikers and rollerbladers as well as walkers.  Numerous parking lots are available along the trail.

Numerous other outdoor activities are available.  The City of Alexandria's website lists numerous area parks and recreational facilities.  Whether you're into nature hikes, swimming or boating, you'll find plenty to keep you occupied.