I'm wondering what kind of stone they used. That "charred" look, the black/grey coating on the stone, is often seen in stone often deemed unsuited for construction or monuments. I see it on limestone in nature documentaries all the time, but I'm inclined to doubt anything built of limestone would still be standing in Scotland after all that time, since limestone is one of the most water-soluble, fast-dissolving common minerals (calcium carbonate) found in large deposits worldwide.
Personally I like the "charred" look, but that coating could be pollutants, mold, mildew, fungus, or any combination of those and other elements. Meanwhile, it does have a weirdly ethereal look, with Greco-Roman style pillars in open space, surrounded by city and then water.
I wonder how many Scottish fiction authors have used this thing as a "gateway to another plane/world/dimension" plot device
. It sure looks like it could be hiding all kinds of doorways...