Head to Fort Union Trading Post and learn about its role in defending against attacks and invasions. This structure has witnessed some interesting history in its time.
This history-filled fortress in Williston comes recommended by many travelers, so put it on your travel plans. Don't think that's all there is to do here, though. There are plenty more places ready for you to explore after Fort Union Trading Post. Missouri-Yellowstone Confluence Interpretive Center, and Fort Buford State Historic Site are not far away.