A few minutes walking around Little Round Top at Gettysburg.
Long moved by the out-of-ammunition bayonet charge of the Union troops to hold the line. The Colonel there, named Chamberlain I believe, later officiated over Lee's surrender at Appomattox. During the charge, a Confederate officer put a revolver in his face and pulled the trigger; it didn't fire.
The site itself seems too small for events of that magnitude: it's just a little hill with trees and tiny rock paths, reminding strongly of, say, the campgrounds in miniature nooks around Mt. Palomar. Americans killed Americans there to try to preserve human slavery.