Which one is being referred to?

I agree that the "which" is ambiguous.
Prior context might give us a clue as to what is meant here by "consideration." This could steer us as we read on.

Sometimes we assume the closer antecedent where both are possible, but don't count on it.
It would be much better to rewrite the sentence, avoiding ambiguity.

I find the sentence perfectly unambiguous. The quality of which refers to the area, not the monument. If it were to refer to the monument, it would have to be reworded: The monument, whose quality / the quality of which demands particular consideration, forms an important part of the area.

CB

Hi, CB.

I think what threw me off in my original parsing was what seemed to be an unlikely collocation,
"the quality of the area." "The quality of the monument" didn't seem much better, but perhaps a little.
I'm more comfortable with the quality of the workmanship.
If you change "quality" to "beauty" (which could apply equally to the monument and the area), there'd

AvangiI think what threw me off in my original parsing was what seemed to be an unlikely collocation,
"the quality of the area."

You are absolutely right, Avangi. I guess I'm just too used to not using my brain when I read something in English and take everything at face value the way things are done in Finnish, for example. Anyway, not everybody has to u

Thanks. You're too generous!

After I read it a few times with your original opinion in mind, I was starting to get used to your reading.