The shadow realm(limbo)
The shadow realm is what you may call an 'in world limbo'. While other types of limbo tend to send you to a place between realms, an 'in world' limbo, like the shadow realm, is a type of limbo that doesn't really send you to a place between realms, but rather traps you within the one you're already occupying. In the shadow realm, time does not exist, like in all types of limbo, but since this type of limbo is 'in world', it's a little bit different. In this world there are no sounds, no weather, and no movement. In this world you can see foggy shapes everywhere, and very technically, they are literally everywhere all at once, because they represent the living creatures in the real world
Since both time doesn't exist, and the foggy shapes represent the living creatures in the real world, the shapes that represent these creatures are everywhere that their real life counterpart has ever been, and ever will be, all at once. Weather you see them or not all depends on perspective. This shadow realm is also plagued with the nightmares of living creatures that occasionally appear, once again, based on perspective(note that the nightmare is what manifests, not the creature having the nightmare). And once again, it doesn't matter when these nightmares were had because in the shadow realm all the nightmares that ever have been and will be, exist at the same time, but are only revealed through thoughts.
And because time does not exist here, directions mean nothing, because in the real world, the landscape is constantly changing and shifting. The landscape of the shadow realm is never consistent, therefore you could do something like walk in one straight line for hours and not move an inch forward, or you could be in a forest one moment, take two steps, and all the sudden your in a frozen wasteland. But, yet again, the shifting landscape is also based on perspective. If you do not believe that you will ever find your way, or are not concerned with your surroundings, you will forever be lost. If you allow your thoughts to wander, and worry about every possible way things could go wrong, the landscape will continue shifting, much like your thoughts, and often times, you do not notice the change in your surroundings until your thoughts return to where you are. If you are fixated on one thing and remain in a single frame of mind, you will remain where you are and you won't get anywhere until you realize you haven't moved an inch. In other words, those who are stubborn never move, and those who are always worried never stay in one place for more than a few seconds.
The shadow realm is also connected to the dark gems in the real world. If you were to perform a ritual with the right spell, and plenty of dark magic, provided by the dark gems, you could send either yourself, or someone else to the shadow realm. However, sending more than one creature to the shadow realm at once would take a lot of power.