Heaven vs mythical place

Heaven and mythical place both are nouns.

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

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

Heaven: a place regarded by various beliefs as the abode of their deities; also a place where good people are believed to go after death
mythical place: a place that exists only in imagination; a place said to exist in fictional or religious writings

Other hypernyms of Heaven include fictitious place, imaginary place.

Heaven (noun)	mythical place (noun)
a place regarded by various beliefs as the abode of their deities; also a place where good people are believed to go after death	a place that exists only in imagination; a place said to exist in fictional or religious writings