open fireplace vs niche

open fireplace and niche both are nouns.

Word	Noun	Adjective	Verb	Adverb
open fireplace	Yes	No	No	No
niche	Yes	No	No	No

As nouns, niche is a hypernym of open fireplace; that is, niche is a word with a broader meaning than open fireplace:

open fireplace: an open recess in a wall at the base of a chimney where a fire can be built
niche: an enclosure that is set back or indented

Other hypernyms of open fireplace include recess.

open fireplace (noun)	niche (noun)
an open recess in a wall at the base of a chimney where a fire can be built	an enclosure that is set back or indented
	a small concavity
	a position particularly well suited to the person who or organization which occupies it
	(ecology) the status of an organism within its environment and community (affecting its survival as a species)