Geological Museum, Madrid. I pass by here often as I live not too far but I haven't been inside yet. I will have a look soon, I promise!

This is the side of the building. Hidden down a narrow and nondescript lane is this mural. Difficult to get a good shot due to the tightness of the angle in the narrow sidestreet and the fact that the sun hardly gets round here.
ADDED NOTE a week later: I got a shot of it in the sun. I'll post it soon. Second thoughts - on viewing the sunny one, this here is MUCH better and more clearly defined! This stays alone!