The song I posted in the OP in particular was inspired by HP Lovecrafts novels. If you know anything about his novels, it's filled with
"deep dark crevice" stuff. In his are based around a creature he created called "Cthulu". He sleeps deep beneath the sea, until he is woken. A huge deep dark abomination of a creature.
Cthulhu (/kəˈθuːluː/ kə-THOO-loo; for variant pronunciations, see below) is a cosmic entity created by writer H. P. Lovecraft and first introduced in the short story "The Call of Cthulhu", published in the American pulp magazine Weird Tales in 1928. Considered a Great Old One within the pantheon of Lovecraftian cosmic entities, the creature has since been featured in numerous popular culture references. Lovecraft depicts Cthulhu as a gigantic entity worshipped by cultists. Cthulhu's appearance is described as looking like an octopus, a dragon and a caricature of human form. Its name was given to the Lovecraft-inspired universe where it and its fellow entities existed, the Cthulhu Mythos.
H. P. Lovecraft's initial short story, "The Call of Cthulhu", was published in Weird Tales in 1928 and established the character as a malevolent entity, hibernating within R'lyeh, an underwater city in the South Pacific. The imprisoned Cthulhu is apparently the source of constant anxiety for mankind at a subconscious level, and also the subject of worship by a number of human religions (located several places worldwide, including New Zealand, Greenland, Louisiana, and the Chinese mountains) and other Lovecraftian monsters (called Deep Ones[10] and Mi-Go[11]). The short story asserts the premise that, while currently trapped, Cthulhu will eventually return. His worshippers chant "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" ("In his house at R'lyeh, dead Cthulhu waits dreaming.")[9]
Lyrics from "The Thing That should not be" the song in the OP
Not dead, which eternal lie
Stranger eons death may die
Drain you of your sanity
Face the thing that should not be
Fearless wretch insanity
He watches lurking beneath the sea
Great old one, forbidden site
He wakens, hunter of the shadows is rising
Immortal in madness you dwell
^^Those lyrics are direct quotes from HP Lovcrafts novel "The Call Of Chtulu". Chtulu is considered a "Great Old One" referring to the Old gods that stir beneath the surface and cause terror and anxiety among society, on a sub-conscious level.