OK, this picture is not exactly of a contraption, but I am taking advantage of the PP promise that we can interpret liberally during this freestyle period. So I offer this:
I came across it in a small town in the West Country during my wanderings. To the side there was a town Council notice which said, 'we have sought planning permission to redevelop this site, meanwhile we have planted this garden for you to sit in and enjoy.' I was so impressed, I went and sat in it. At the rear, there is a fence, and I discovered that behind it, the Council had stored all their construction machinery and contraptions (aha!).