Hello @everyone:

The 12th Post Processing Contest by @bambuka has run out without my puzzle being fully solved....

@lllll1ll, however, with a good eye for structures and shapes, has recognised the essential: a wheel or a tyre. But then she also took the wrong direction and thought about what kind of surface it might roll on...

It doesn't - probably this detail was the real mean thing about the choice of my motif: the wheel belongs to the landing gear of a small aeroplane. I photographed it from above, out of the plane, when it was about 600m above the ocean ;-))