The Construction Playground in Basel, Switzerland was completed in 1972 on a former orchard on the Rhine.
As Marguerite Rouard and Jacques Simon put it in their wonderful 1977 book, Chldren's Play Spaces: from sandbox to adventure playground:
The area is open at certain hours by a supervisor whose barracks serve as an office, Red Cross station, and playroom for rainy days. The building material consists of boxes from industrial plants. The shacks and other structures are in most cases clearly visible and the residents of the neighborhood have gotten used to a certain amount of disorder and construction confusion.