The windows on the top floor of Everett Mill produced some absolutely fascinating light thanks to the fact all of the ones on the west side of the building were covered in canvas, presumably to cut down on solar heating. The covers had browned with age and were stained in places, producing interesting patterns and a fascinating, golden light within the building.
You can see another shot of these windows here but this version is a rather different take on the subject courtesy of a fisheye lens.