Xander van Vliet
Here we see an impossible sand mill based on Escher's Waterfall. Instead of water in original image, here endless stream of sand drops into the sand glass. It will never been filled, because there's no bottom in the sand glass. All sand goes down the sand river to the top of the sand fall to fall into the sand glass again.
Another impossibility of the artwork is the mirrored copy of the sand fall, which stands on the column of the first one. Going by the copy of the millT, the sand falls upwards.
The image was found at http://www.pythagoras.nu/gallery/Escher98/uit17.html