Bit of a story for this. Based heavily on a photograph given to my father quite a while ago of an empty office space with some beautiful shadows falling through the windows. Having scanned the photo, I set about exactly recreating the scene in blender. This I then devolved into the strangeness that you can see here. Playing with caustics in this scene was quite fun, and tweaking the sunlight to match the original photo exactly was certainly an experience. I guess if you don't hoover the carpet, this is what happens when the dust builds up...