This is one of my favourite illusions because it is so simple and yet so effective.

This is constructed entirely photographically from about sixty photographs chosen from over two hundred taken for the image.  These were used to texture and accessorise a pre-prepared geometrical construction. The people were later posed and photographed to fit their eventual positions.

A key element in this illusion is the contrast of warm lighting to define the underside of the stair and cool lighting to define the top.