During the King's Quest series a handful of various realms often associated with death or the afterlife from myth and legend are mentioned throughout the series (and spin off literature).
The manual of KQ6 states that;
"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."
From Davey Jones' locker, Hell and Abram's bosom, and Father Death mentioned in KQ4...
A rather grim reaperish version of Death appears as a picture in the KQ2 manual.
Heaven (assorted references throughout the series)
Hell is mentioned in KQ4, KQ8 and the Companion.
Realm of the Dead/Underworld (KQ6) The KQ6 hintbook even aludes to a place called the Abyss... Mount Olympus is alluded to as a heaven of sorts, for example.
KQ8 mentions several places, the Dimension of Death, the Realm of the Sun (essentially Heaven), the Chamber of Enlightenment (It is the home of ancient spirits, aka spirit-world of the ancient souls), and the black Abyss (a swirling bottomless vortex first mentioned in KQ6 Hintbook)... http://kingsquest.wikia.com/wiki/Abyss
Hades (ruled by Pluto), Hell (Satan is mentioned) and the Welsh version of the Underworld, ruled by King Arawn are mentioned in the King's Quest Companion...
Ooga Booga land in KQ8 is also described as an afterlife of sorts for those who die in the Realm of Eldritch, where they go on exist in undeath, as the citizens of that realm. This appears to be made more clear in the Companion, where Malicia seemingly calls it the Land of the Dead.
It seems that Roberta, and others had an often pluralistic view of her universe... Similar to how the Cole's incorporated the egyptian afterlife of Tu-at (including Anubis) in QFG3, and both Hell and Hades in QFG5.
Of more interesting note, is that in an early version of KQ8, apparently the Abyss would had a bigger role... In the released game the black "Abyss'' is the dark swirly vortex realm that Conner banishes Lucreto into...
In some of the early concepts, Conner would have apparently visited the realm himself, then known as 'the dark abyss'. He would have required a certain piece of the mask in order to see in the darkness. How he would have made it into the realm is unclear. It may be possible that the name and location have been associated with one of the other ideas that were cut (perhaps it was an early version of the Dimension of Death, or maybe it was another description for the 'utter darkness of Paradise Lost', or even an dark underwater abyss in the ocean level). But as of yet, these details are unknown.
In the final game, it is portrayed as a bottomless swirling vortex (taking on the more literal description in the Bible where the Abyss is described as a 'bottomless pit'). It became the final prison for Lucreto, much like the Phantom Zone in Superman, Lucreto was sucked into it, banished and vanquished for eternity. In an alternate ending of sorts, Conner can also be sucked into it, leading to one of the more interesting death scenes in the game (as he screams and spins down the black hole)!