Annwn vs fictitious place

Annwn and fictitious place both are nouns.

Word	Noun	Adjective	Verb	Adverb
Annwn	Yes	No	No	No
fictitious place	Yes	No	No	No

As nouns, fictitious place is a hypernym of Annwn; that is, fictitious place is a word with a broader meaning than Annwn:

Annwn: (Welsh mythology) the other world; land of fairies
fictitious place: a place that exists only in imagination; a place said to exist in fictional or religious writings

Other hypernyms of Annwn include imaginary place, mythical place.

Annwn (noun)	fictitious place (noun)
(Welsh mythology) the other world; land of fairies	a place that exists only in imagination; a place said to exist in fictional or religious writings