hell on earth vs the pits

hell on earth and the pits both are nouns.

Word	Noun	Adjective	Verb	Adverb
hell on earth	Yes	No	No	No
the pits	Yes	No	No	No

As nouns, hell on earth and the pits are synonyms defined as:

Other synonyms of hell on earth include hell, hellhole, inferno, snake pit.

hell on earth (noun)	the pits (noun)
any place of pain and turmoil	any place of pain and turmoil