netherworld vs mythical place

netherworld and mythical place both are nouns.

Word	Noun	Adjective	Verb	Adverb
netherworld	Yes	No	No	No
mythical place	Yes	No	No	No

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

netherworld: (religion) the world of the dead
mythical place: a place that exists only in imagination; a place said to exist in fictional or religious writings

Other hypernyms of netherworld include fictitious place, imaginary place.

netherworld (noun)	mythical place (noun)
(religion) the world of the dead	a place that exists only in imagination; a place said to exist in fictional or religious writings