I used the darktable Color Zone module for monochrome conversion on this ghostly image.
Color Zones > switch to black & white > saturation mode > pick the ‘blue’ from the sky > change to lightness mode > reduce the blue from the sky to zero > pick the building color > bring up building color lightness to full
Also tried the (or better had to use) the spot removal module for the dirty sensor.
Fun to play!
(The factory is in Shipai, China. That’s between Shenzhen and Guangzhou. When you take the train from Shenzhen to Guangzhou you can see it on the right side near Guangdong Station. 石排恆基水泥廠/原東江水泥廠)