I know there are other, more significant battlefields, but for me, Lexington, MO is evocative (maybe because it was one of my first). It's been a long time since I've been there, but I still relate things back to that site.
The trenches were still there, although little more than shallow depressions fronted by rounded humps. Anderson House, which was used as a field hospital by both sides, still had marks on an upstairs railing where, according to the park ranger, rebel prisoners were hung (okay, ALLEGEDLY hung), and there were stains in the floor from blood that dripped from the tables. The scope of the battle wasn't all that much, compared to places like Gettysburg, Antietam, or Shiloh, but its preservation was excellent, and the artifacts were (when there weren't a lot of tourists, and the ranger was feeling magnanimous) still touchable with close supervision. It's something big to a kid to put on a kepi that's got a hole and a huge brownish stain on one side of the cap and to know where it came from.
There were more recorded Civil War battles in Missouri than in Virginia; likely more short, brutal raids and ambushes as well. The Missouri Soldiers Database includes 380,000 listings for the Civil War; and Lexington's Battle of the Hemp Bales is still very closely considered for Confederate General Sterling Price's decision to delay his attack on the Union fixed positions until his full supply train had arrived. Junior officers and amateurs study tactics and strategy- real professionals sweat the logistics.
Return to the place of that first visit of yours, my FRiend; next year if not during the September anniversary of that old fight. There are still lessons to be learned there.
You ever notice the name of Rooster Cogburn's cat in the John Wayne movie True Grit?