and there is lots to see right there as well, and also wonderful restaurants, many with outside venues in nice weather. We were there slightly before the spring tourist season - I think it must have been in March, and not all of the water ferries were running yet, or maybe we just didn't have time, can't remember, but I think you can also take a ferry from Alexandria over to Mt. Vernon - but could be wrong on this one.
There were also water taxis. Google this stuff or look on Trip Advisor.
We did a paid walking tour of Alexandria one day that left from the visitor center. Also walked down to the waterfront (Potomac) and happened to see the space shuttle being flown up (or down) the river to Dulles prior to being installed in the new building that I think is part of the Smithsonian Air and Space museum. How cool was that? Just followed a bunch of people walking out of their convention meetings at lunchtime and asked what was going on. We tend to be a little out of the loop when we are traveling
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D.C. has so much to offer that a trip every 3-4 years there, and probably staying in different places, is a great idea. Just seeing that beautiful city gives a great feeling of national pride. What a showplace.