The Four Underworlds are the four levels of Death in the Garryverse, heralded by bedrockperson. They are strongly influenced by early Judeo-Christian teachings about the afterlife.
P'sach DenP'sach Den (פְּסַק דִין, pronounced "P'sɑch D'ēŋ") is the first Underworld. As the name suggests, it is a place of judgement. Those who are judged righteous are sent straight to She'ol, those who are not are sent to Gehenna.
GehennaGehenna (גהנום) is a place where most of the wicked are punished, to a degree. Residence in Gehenna is never permanent, and can last as short as a year.
Tzoah RotachatTzoah Rotachat (צוֹאָה רוֹתֵחַת), or The World of Bone, is a place within Gehenna reserved for the most vile of sinners. It is the absolute final resting place for all evil. Torture and punishment are never-ending in Tzoah Rotachat. Here, beings such as Adramelech and Anomaly XJ-9041 are commonplace. It is the "official" domain of Gascot, as Ha-Satan.
She'ol (שְׁאוֹל) is the final resting place for all, sinner and righteous alike, excluding those condemned to Tzoah Rotachat. It is a peaceful place of forgetfulness, cut off from all life and God himself. Its inhabitants, the Rephaim, are soulless beings without strength and true minds.While this existence is bleak, a place of holiness does exist within She'ol. Known as "the Bosom of Abraham", the Sheol contains a place of comfort and stability where the righteous can be one with God. This place is the dominion of Angels and God himself.