I seem to have almost natural affinity for darker places.. But then again, for various reasons, it's so much easier to publicly tell stories about darker and sinister ones, rather than the lighter and more innocent domains/planes. Anyone would probably have their own different take on what it is and how it looks like, so this is more like a short intro on certain plane of existence (or non-existence) that I conveniently call "the Void".
Void is the bottom layer, that collects all that was lost and forgotten. I personally believe all road and paths eventually lead to void. But while very bottom of the oceans is quite a distance away, it's not exactly the same with the void, it's always very near, at least for those of us that dwell a bit higher, but our existence for those who find them selves stuck in the void - is almost infinitely far, almost unreachable in most cases.
While Void, to the most part, should be place of non-existence, life always find a way. There is certainly "life" there, even if often bizarre by our standards, sometimes even grotesque. Life that learned to live on scrappiest scarps, and life that have not ever known concepts karma, morals, good or evil, or even if they known any of those, they long forgotten everything. It's the law of the jungle in it's purest, most raw form.
There is no light there, yet once your eyes adjust to that thick blackness you might start to different shades of the black. But you might see some specks of light in a distance, don't be deceived, all the light there is false. Almost like all the light in deepest parts of our oceans is just bioluminescence coming from predators, so in the void it's better to keep your distance from all the "light" there.
And then void have some other "features". Once you enter Void, Void enters you, and all that was hidden and suppressed within, tend to come out. All your fears, shames and insecurities, all your demons, Void will give form and shape to it all. It will manifest all your nightmares on the spot in a very high resolution and more. So it would be highly recommended to do a lot of homework on self, for all adventurers planning journey in to Void, beforehand.
Despite the name "Void" and general notion of "non existence", void does have strange and bizarre pockets of existence here and there. But "life" in those usually take very "unusual" forms, there often "creatures" that neither dead nor alive by any known definition. Some of it even looks like something or someone tried to create life from just distorted fragments of memory of what life should look like. "Silent Hill" comes to mind, not 100% accurate but they got pretty close to the general vibe.
May you have exciting adventures and be back with nothing missing, nor with anything extra!