Hell

Hell (or deepest hells) is the dark underworld reserved for those who are evil in some philosophies in Daventry, including the Christian beliefs.

Background
Death fascinates men the world round, and there are as many philosophies about what comes after this life as there are, it seems, lives which end. Hell is just one of these beliefs. It is ruled by Satan. Sinners may end up going to hell, and demons are often associated with hell. In some beliefs there are more than one hells. Wicked denizens live in the deepest hells listening to infernal music. Some belief that the dungeons of hell can be seen hanging from the floating portions of Mordack's Island, magma from there drains down to the land below.

William Shakespeare wrote in Hamlet that at witching time of the night, churchyards yawn, and hell itself breaths out its Contagion into the world. The Zombies in Tamir are evidence of this phenomena happening in the world.

Graham was sure Mordack's hideous organ in his castle played music only for the denizens of the deepest hells.

Behind the scenes
Hell or Hades is mentioned or alluded to in two comments, one is the reference to Abram's bosom, and the other is the Complete Works of Shakespeare.