We stayed a night in Wuppertal on our way to Dortmund airport to catch a plane to Plovdiv. We only saw the city in the dark, but we did get to ride the "Schwebebahn" - a hanging tramway. Nothing too exciting, but a nice experience. The train travels along the winding river Wupper that flows through the city. The idea makes sense in using the space above the river which is otherwise lost.
I have no comment to make on the city. We walked around the city centre, which seemed nice, but a little dark. Maybe due to the energy saving measures. We did have a nice dinner in an asian "street food" cafe.