Like all underground transportation systems in the world, the French metro makes ends meet by selling advertising space. This, since... 1947 (and a little before too)! Generally rented by the week, this space has seen thousands of ad campaigns since then! One artist - Pierre-François Grimaldi - had the idea of turning them into real pictures. Some of them can currently be seen at Galerie W, near Montmartre. Quite clever - and interesting for "old" Parisians like me who may remember some of these campaigns!