If you want a small town feel, a historic old European city feel, and still be near a big city, then you will understand why Old Town Alexandria keeps getting voted as one of the best small towns in America. It is really cute. It has free busses and a free trolley from the subway stop. Also, it is on a subway line that connects to two airports.
I just like how quaint it is (oh, and I love the dairy sold at the farmers market — the market is from 1753 and is the oldest continuous farmers market in America. It is every Saturday from 7-noon). Several of the blocks in the heart of the waterfront area have been made pedestrian only. Many restaurants line these blocks and it is a pleasant place to eat, socialize, and people watch. The boardwalk/quay is nicely made and there are both toilets, drinking fountains, and benches all within easy reach.
If you visit, try going during the day and visit the Torpedo Factory, an old factory turned into artist studios and shops. There are also many tours of Old Town, covering history, food, and ghost.
The streets are tree lined and a few still have the original cobblestones. This is an old city so you may need to walk arm in arm on the uneven sidewalks.
