Naraka, or hell, is the lowest of all realms and consists of the eight great hells where one can reincarnate depending on past karmic actions. Anyone that reincarnates in hell has invoked extremely negative karma so severe that it bypasses all other realms and causes them to be reborn in a realm of perpetual punishment. Beings in hell manifest within Naraka rather than being born.
The eight great hells are depicted as subterranean planes layered on top of one another, and the suffering that one experiences increases in magnitude as you go deeper into each of the hells.
The first hell, Sañjīva, includes torture through hot iron weapons cutting and stabbing one's body while perpetually reviving to go through it again until bad karma is exhausted. Those who committed physical violence such as murder end up here.
The second hell, Kālasūtra, includes the same tortures as the first but with the pain being amplified ten times. Black lines are drawn on the sinners' bodies, and the hell guards carve according to these lines while the sinners are fully aware of the pain. This is the place for those who have committed murder, robbery, or lied.
The third hell, Saṃghāta, involves being crushed by large rocks into bloody mush repeatedly until bad karma has been exhausted. Those not turned into mush have their mangled bodies eaten by demonic animals while being hung with hooks in the air. Rebirth here is caused by an improper attitude toward love and sexual indulgence combined with acts of murder.
The fourth hell, Raurava, is where the hell wardens pour molten metal down the throats of sinners. The primary reason for rebirth here is the improper intake and use of intoxicants in combination with acts of killing, stealing, and sexual indulgence.
The fifth hell, Mahāraurava, is for those who committed perjury or bribery. They are tormented by having snakes born inside their bodies. This is the hell in which the psychological state of the sinner is considered more than the physical act of bad karma.
The sixth hell, Tapana, is where hell wardens impale the residents on a fiery spear until flames issue from their noses and mouths. They are thrown onto a burning iron surface and beaten until reduced to a mound of flesh, fried in a skillet, or impaled and roasted until the flames pierce their bones and marrow. As the first purely mental hell, it addresses the major obstacles to enlightenment.
The seventh hell, Pratāpana, is where demons with black bellies, flaming eyes, and hooked teeth haunt those reborn here, grabbing residents by the throat and dragging them through mountains and cities. Hell wardens put worms inside the sinner's body that burn the innards and excrete poison. This hell is destined for those who have sexually defiled religion — including seducing monks, nuns, and virtuous laywomen.
The eighth and deepest hell, Avīci, is where sufferings are a thousand times more severe than those in all former hells combined, making the inhabitants of those other hells seem as happy as the most blessed deva. Every sinner's odor smells of foul stench, and the sounds of this Naraka would cause those who hear it to die of terror. This hell is the destined place for those who have committed one of the Five Great Offenses of Buddhism — the murder of one's biological mother or father, evil intention of causing harm to the Buddha or the Buddhist community, and the murder of Arhats.