Building No 23

I saw this wonderment in Marseille when my feet were hurting so much that I wanted to lie down on the pavement. We had taken a stupidly long walk on a madly hot day and there were no buses due to a bike rally along the coast path.
If I had had more stamina I might have cheekily asked the owner of the house a bit about it, but it was just a quick snap and then dragging our feet up the hill, hoping we might find a bar at the top.
I especially liked the bricked up window and shutter fashioned out of whatever the concrete/sandy substance is. I think they even moulded a little house martin's nest in one corner of the window.