Wiesbaden has a “mountain” (more of a large hill) with a little train car that goes up and down it called the Nerobergbahn. (I’m pretty sure the “bahn” part means train.) We took the kids up there on Labor Day, since the weather was nice and it wasn’t crowded, as it’s not a holiday for the Germans.
It was a fun afternoon, and a fun experience for the kids. Not bad for €6.60 for all of us, or about $9.25.
Read more about the Nerobergbahn here.