The Manassas Museum is well worth the visit if you enjoy the civil war. For kids younger than 12 they may not enjoy it because there is a lot of reading and original photos to look at.
The museum was created by artifacts the local people donated to it. For me this makes it quite interesting.
It is a small museum so you problely could see it all in 2 hours.
There are some nice restaurants within walking distance. If you eat at Foster' grill and eat outside you can watch the trains pass through Manassas. It is near the train station and within walking distance of the museum. All the shops in Manassas are within walking distance of the museum.
The entrance fee is quite low $5
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