The city stretched before me, muted and empty. Glimpses of life flickered in the corner of my eye like shadows on the wall of Plato's Cave. The only thought I could concentrate on was this: I have to get out of here.
Many religions hypothesize on what the afterlife is like, but pay little heed to the reality that exists in parallel to their own. It's a mirror of the corporeal world, only the sky is a black void and the colours of nature are faded. There is no sign of the living beyond ghostly blurs or flickers in the corner of one's eye - the living are now to ghosts what ghosts are to the living. All humans will eventually have to journey through this lonely realm. Upon death, a person's ghost awakes in the etheric realm in the parallel position of where they died. From there, they must make the long walk over land to the nearest gateway to the afterlife. There are only a handful of these in the world, all located deep in the earth. A ghost might have to travel thousands of miles to reach the gate. This is the purpose of a soul guide - to show their human the route to the afterlife. Catholic tradition describes the etheric realm as purgatory. It is the long walk through a dark land that we must struggle through to reach heaven.
The geography of the etheric realm is identical to the real world. It is like an onion skin layer pulled over the world to cast it in a different light. The general shape of the landscape is identical, though individual details may very. There are forests in the same place, but trees can be different to take into account a tree getting chopped down in one world but not the other. Similarly, cities in the etheric realm tend to lag behind construction in the real world. A house built in the real world might take several days to a week or two to show up in the etheric realm. When no one is looking, the house will just quietly appear where it belongs. This also happens in reverse if something is demolished. You never see, for example, a single brick floating in the air as it's moved in the real world. The etheric realm just quietly shifts things around to better match the world it mirrors.
Fauna & Flora
Beyond the darkness, the main thing that makes the world unerving is that there are... things out there - creatures that lurk in the shadows and roam the empty plains. They tend to stay away from large collections of ghosts, and there are no known cases of a ghost being attacked by one... but it's hard to say with any confidence that it's never happened out in a remote area where a ghost was all alone on their way to a larger highway. Not all creatures are fearsome, though. You might see a unicorn roaming near the edge of the forest, or rest for the night near a muscaliet curled in the roots of a tree. These creatures are not well-known, as study of the etheric realm by the living is challenging and the dead rarely are able to transmit their findings back. Plant life is much the same as in the real world, although they often grow in unusual colours. This does not seem to make sense because there is no sun, but grass continues to grow and trees reach to the empty sky. There are some unique plants to be found; for example, many believe ghost vines originally grew in the etheric realm but managed to break through thousands of years ago to spread in the real world as well.
It is important to note that ghosts are not entirely stuck in the etheric realm. With conscious effort, they can project themselves back into reality. While they are physical in the etheric realm, they are merely intangible images in the mortal realm. They can speak and listen, but can only physically interact with the world through concerted effort and concentration. Being as insubstantial as a wisp of smoke is not comfortable and takes constant effort, so most ghosts remain in the etheric realm unless they specifically want to haunt a person.
Ghost world, ethereal plane
The following shows an example of how the three categories of people perceive the world. In the images, the women at the cart are non-Sighted living people. The girl with the bucket is Sighted. The soldier is a ghost.
A Sighted person sees the mortal world, but also sees hints of the etheric one overlayed on the mortal world.