"Ein Vierteljahrhundert Mathematik" (25 Years Mathematics) by
Ian Stewart, Spektrum der Wissenschaft (2003).
The Boy surface is an immersion of the projective plane, a non-orientable surface. The image enhances the structure of the self-intersection of the surface including the single triple point.
The image is used as cover image of an article by Ian Stewart in Spektrum der Wissenschaft: 25 Years Mathematics.
More on the Boy Surface: come back soon ...