One thing you may have noticed about Fort Union is there's no evidence of walls around it, because of course there were no walls. Hollywood has given us the impression that all Western Army forts had high log walls around it but the fact is a lot of them didn't. And if you look around the western plains you will notice that sometimes you're a long long way from a big tree.
Something I also thought was interesting was that Fort Union was an actual working Fort not just a small outpost in the middle of nowhere where the soldiers had nothing to do except March, drill, and keep an eye on the local Indians. Fort Union was like a town it had all kinds of people in it doing all kinds of different jobs and was a major resting point for travelers on the Santa Fe Trail so, there would be a lot of civilians as well as military at the Fort as the wagon trains came through.
I really enjoyed my visit to the Fort Union National Monument because I've always loved Western history and I have a good imagination. And the skeletal remains of Fort Union require a lot of imagination.