We visited Bannack State Historic Park in August 06. It was a beautiful day and we expected a lot of other tourists to be there, but we had the park practically to ourselves, which made it even better. A lot of buildings are open and you are allowed to walk inside them. They have been left in a state of disrepair and all the rooms are empty (this is an authentic ghost town, not a redesigned one, so don't expect it to look like it was in its heyday.) And yet this is fun for the imagination - as you walk through the houses, you find yourself trying to picture the people that lived there and what their lives were like. Definitely pick up a written guide so you can learn about the history of each building - this is what brings it all alive.
My toddler and preschooler did get a bit bored after awhile because we kept them in the stroller (I didn't want them running loose because there are too many potential hazards for little ones) but my two school aged kids seemed to find it interesting. So I would say it is better for older children, in my opinion.
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