I wouldn't call the Williamsburg Historic District an "open-air museum". I'm sure that most likely refers to places like those dinosaur themed museums/parks you see along the highway or other tourist trap-like things. I'd tag something like that under the same umbrella as a proper theme park like Busch Gardens, but not a historic site like the Williamsburg Historic District. I'll tag this as a park since it's a more ambiguous tag and the area technically functions as one.