Just as the world of spirits is a state halfway between heaven and hell within us, it is a halfway place. The hells are underneath it and the heavens above it.
All the hells are closed on the side that faces that world, accessible only through holes and crevices like those in rocks and through broad gaps that are guarded to prevent anyone from coming out without permission, which happens in cases of real need, as will be discussed later. Heaven too is bounded on all sides, and the only access to any heavenly community is by a narrow way whose entry is also guarded. These exits and entrances are what are called the doors and gates of hell and heaven in the Word.
The world of spirits looks like a valley surrounded by mountains and cliffs, with dips and rises here and there. The doors and gates to heavenly communities are visible only to people who are being readied for heaven. No one else finds them. There is one entrance to each community from the world of spirits with a single path beyond it; but as the path climbs, it divides into several.
The doors and gates to the hells are visible only to the people who are going to enter them. They open for them, and once they are opened you can see dark, sooty caves slanting downward into the depths, where there are still more gates. Rank, foul stenches breathe out from them, stenches that good spirits flee because they are repelled by them, while evil spirits are drawn toward them because they find them delightful. In fact, just as we find delight in our own evil in this world we find delight after death in the stench that corresponds to our evil. We might compare this with the delight of carrion birds and beasts like crows and wolves and pigs who fly or run toward rotting corpses as soon as they get wind of them. I heard one man who screamed aloud in utter torment at a breath of air from heaven, but was calm and happy when a breath from hell reached him.
from Heaven and Hell, Sections 428, 429