It's quite incredible how close Poland and Germany are culturally. And how unaware both countries are about this.

Are they really unaware or do they actively deny the cultural connections? Prussia was a thing not that long ago - it is still used as a slang term for Germans in parts of the Netherlands ("de Pruisen" of "die Preußen"). Anyone who had a bit of history or who has looked at an older map sees that Prussia was divided between what is now Germany and Poland. Of course both countries went through a lot of upheaval between then and now but there's still plenty of people alive who will remember living in Prussia.