The void
ID: A skykid in the void looking at figure of light in the dark, dark distance.
The void is an enigmatic place best described as a memory-space located between life and death — between the earth and the equally mysterious "orbit". The void is not a physical location and can only be reached with one's conscious. It is often visited unintentionally by ancestors/skykids whose lights have been extinguished and have not yet returned to orbit (whether it be because they're not dead yet, or some extraordinary circumstance). The void can be visited intentionally by meditation, though there are external factors which decide if one's conscious will be successfully transported to the void.
ID: the void, depicted as a series of bubbles, some large and some small, loosely floating around each other but not being connected. Some of the larger bubbles have drawings inside. Beneath the map of the void is a skykid meditating by some crystal shards. The drawing shows the act of meditation potentially taking ones' conscious to 1 of 2 different locations within the void.
The void itself can be thought of as a collection of pocket realities, rather than one unified location. One can visit certain void pockets by meditating in areas associated with strong memories. For example, meditating by a red darkstone shard will often transport one to void pockets associated with Eden (or the disaster that happened there). Void pockets associated with "weaker" memories, like the memory of a single person, can be harder to reach especially without personal connection to the subject. Void pockets associated with something or someone noone in the world has memory of are impossible to reach.
The contents of a void pocket depend on the memory it is associated with. For example, the void pocket associated with a single person will likely contain things relating to them — perhaps objects they owned, people they care about, or even small scenes depicting locations of importance (like a portion of their home). Because the contents of a void pocket is influenced by the memories of the living and unliving, it is possible to influence their contents assuming one can control the memories. The primary examples of this are the Elemental Trials.
ID: A drawing of the Prophet of Water thinking really intensely. In doing so, it causes the void pocket associated with them to change to their liking. They think, and therefore it is.
The expansive and strange nature of the Elemental Trials compared to other void pockets are due to two factors, 1) the Prophets' status in life and 2) the Prophets' awareness of the void. Their elevated status would allow their void pockets to be bigger, but more importantly, awareness of their respective void pockets allowed for greater control of their contents. As the "subject" of their void pocket, their memories have the greatest influence of their void pocket's appearance and behavior. With this knowledge, the Prophets could shape their void pockets' environment to their liking, complete with "rules" those visiting must follow (namely, disallowing the use of magic), thus creating their respective trials.
While in a void pocket, objects within can be interacted with, but cannot be taken outside of the void. Using the Trial of Water as an example, successful trialgoers are bestowed a concentrated amount of blue light, allowing them to walk on water. Once they leave the trial (and thus the void), they will no longer have the blue light on their person, and thus lose the ability to walk on water. This does not mean all things bestowed in the void cannot be taken into the living world. The void pockets associated with the Elders are an example of this.
In the living world, there are some mechanisms (mainly doors or gates) which are said to only operate for those who have the Elders' blessing. In their not-alive state, the only way to receive their blessing is meeting them in the void (and what the Elders are doing in there is a discussion for another article). After doing so, the physical mechanisms in the real world will work again. In general (and in less supernatural cases), knowledge, wisdom, or other nonphysical gifts gained in the void can be taken back and applied in the living world.
ID: A 2 panel comic. In the first panel, a skykid is surfing across the water in the Trial of Water thanks to a spell. They think to themself, "Man! This water walking ability will be useful once I get out of this trial...!" The next panel depicts the skykid, no longer in the trial, flailing in the water, exclaiming, "BANARI HEEELP, I CAN'T SWIMMM". A skykid on the coast calls out "What are you doing!?". The original skykid exclaims, "I THOUGHT I COULD STILL WALK ON WATERRR"