We've lived in Fairfax County for 28 years and until last weekend, had never been to Huntley Meadows. But, one of my co-workers has spoken of it quite often so we decided to try it.
After a fairly short walk through the woods, you come to a fresh water wetland. (When I was growing up, these were swamps.) The County has done an excellent job of making the swamp accessible and educational while preserving the nature of the place. The best thing to do while in the swamp is just stand still for a few minutes. You'll be amazed at what you'll see.
Another remarkable thing is that this close to US Route 1 and the Capital Beltway, there can be dead quiet.
Highly recommended for families with children or couples who want to take a leisurely walk.