This recent BBC article features an exhibition of photographs taken by French photographer Jason Guilbeau from Strasbourg. Guilbeau spent time travelling around the sites taking images of the various forms of architecture...also capturing the various forms of decoration added in more recent days. Personally, I abhor graffiti and would much rather see them painted grey than be covered with the names of some wannabe-gangster-kid who thinks he is all that.

Anyway, the images are in the link below:

BBC - Future - The surprising and eerie beauty of World War II bunkers