This is the 11887th most frequent Polish word.
królestwie
"Królestwie" means "kingdom" (locative case).
Here, "królestwie" is used in the locative case as part of a prepositional phrase indicating a place where the action occurs.
W królestwie tym żyły przeróżne stworzenia.
In that kingdom, various creatures lived.
In this sentence, "królestwie" reflects its usage in the context of being part of an ancient historical entity, again in the locative case.
Hełm został odnaleziony w starożytnym królestwie.
The helmet was discovered in an ancient kingdom.
The word "królestwie" is utilized to refer to the domain ruled by the subject, implying sovereignty and governance.