The Muppberg rises just across the Bavarian side of the border near Neustadt bei Coburg, close enough to Sonneberg to count as a local outing. It is a wooded hill rather than a dramatic mountain, but the lookout makes sense if you want to see how tightly Bavaria and Thuringia press together here.
Go for a walk, not for spectacle. The Muppberg is best as a simple breath of forest air after museums and town streets, especially if you are travelling by car through the border region.