What are the taboos of the Hill People? Why are these things forbidden?
It is hard to escape the conclusion that, from the very first lines of this masterful short story, we are plunged into a primeval, primitive world, where man is ruled by ignorance and taboos without explanation. The repeated reference to "rules" and "laws" and in particular the number of times that the word "forbidden" is repeated clearly underlines this aspect of the society of the narrator: it is a civilisation that is constructed around a carefully regulated system of laws and creeds that give clear boundaries to humans.
I will point out some of the taboos, and then you can discover the rest:
The north and the west and the south are good hunting ground, but it is forbidden to go east. It is forbidden to go to any of the Dead Places except to search for metal, and then he who touches the metal must be a priest or the son of a priest. Afterward, both the man and the metal must be purified. These are the rules and the laws; they are well made. It is forbidden to cross the great river and look upon the place that was the Place of the Gods - this is most strictly forbidden. We do not even say its name though we know its name. It is there that spirits live, and demons - it is there that there are the ashes of the Great Burning. These things are forbidden - they have been forbidden since the beginning of time.
The first paragraph, then, clearly paints a picture of the world we are in - a world with taboos to protect their people from, as they see it, demons and spirits, though clearly having read the story the reader is able to identify the true nature of the "Great Burning" and the radioactive dangers of the nuclear holocaust that has moved mankind back so far.