Astral Plane

The astral plane, also called the dream world, is a non-physical realm that seems to be where all the dreams and memories of humanity are stored.
It is difficult to gather information about the astral plane, as it is very mysterious. Some have been able to reach the astral plane through a process called starwalking, but even from their records, there are many questions unanswered.
Starwalkers have described the astral plane as an unpredictable environment. The landscape is not stable, but not in a physical way - one's entire surroundings may change and one may wander in and out of memories at random. 
Memories themselves seem to play out in parts of the astral plane, and starwalkers can observe these, although they have described it as difficult to get any knowledge out of these memories since they have no way of knowing whose memories they are or when they are from. Starwalkers have also observed scenes that seem to be dreams playing out. Some have even managed to communicate with others through dreams.
Occasionally, starwalkers have viewed memories from the perspective of a person in the memory, rather than as an outside observer. This usually only happens with their own memories. They have described being so immersed in the memory that they forgot that they were in the astral plane until it was over.
Nothing from the astral plane can be taken back into the physical world. However, objects from the physical world can be taken in and out of the astral plane - such as a starwalker's clothing.
The astral plane has been theorized to be made entirely of aether. If a glyph is drawn there, it will cast immediately, without aether having to be drawn in - so, at the very least, there is a lot more aether in the astral plane than in the physical world.
It is unclear where the astral plane came from and whether or not it existed before aether. Starwalkers are trying to discover when the astral plane may have begun by trying to find the oldest memories stored there, but this is very difficult, and the secrets of the astral plane may remain undiscovered for a long time.