Rheinpark Duisburg
The Rheinpark Duisburg [↗] is an old industrial area that has been converted into a recreational park. It was originally intended to host the Bundesgartenschau (Federal Horticultural Show) 2011. But Duisburg withdrew for financial reasons. Instead, the area is now a 25-hectare meadow landscape with more than 3000 newly planted trees.
The part of the Rhine Park we're talking about here is primarily a recreational area (the whole area is much bigger and has some residential areas too) including sandy beaches on a promenade along the Rhine with wooden plateaus for laying at the beach and other a skate park and a streetball court.
We visited this place before we went to the Zeche Zollverein. The main reason wasn't to go for an easy walk in the morning, but when creating the park, they left a couple of walls from the former industrial buildings. Those are decorated with a huge number of graffiti. Quite some of them are still in good condition.
The park is easy to get to and if you come early on a working day, very few people are around and parking is no problem. This is most probably different when you come in the afternoon or on a weekend.