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This reversible figure is calle the Schroder Staircase
You are probably seeing the staircase as sitting on the ground such that you could walk up the stairs to the right. Now, try looking at the upper left hand part of the image, and imagine that it is the closest thing to you in this picture. Suddenly, the staircase flips, and it is as though you are seeing the stairs from below.
Again, the cause of this illusions is a lack of 3d context for this ambiguos 2d drawing. It is possible (but difficult!) to see this picture is a purely 2d drawing without any 3d features at all. It should looke something like a skewed diamond shape with zigzags in the middle.