Frogmore Cotton Plantation & Gins is a working cotton plantation across the river from Natchez, used as a historic site to explain how cotton plantations operated before and after the Civil War. The preserved buildings and gin equipment make the scale of the old cotton economy easier to grasp than a mansion tour alone.
It is a sobering stop, because plantation history here also means slavery and forced labour. Go for the context: it pairs well with Natchez's grand houses, but tells a harder and more useful part of the story.