The Zone of Darkness[1, 2], also called the Zone of Shadow or Field of Shadow, was the place where the Visorak hordes contained the Zivon. Kahgarak were able to open a gap in the Zone of Shadow with their Rhotuka spinners, allowing the Zivon to emerge. Kahgarak were also the only thing that could send the Zivon back, preventing the horde from being wiped out by the Zivon's appetite.
The Zivon lived in a dimension of perpetual darkness which could be tapped into only by the power of the elite Visorak.
Very little was known about the Zone of Darkness, other than that it could apparently be accessed by the Rhotuka spinners of Kahgarak and that it was the natural domain of the Zivon.
Kahgarak Rhotuka were the only way to reach the Zone of Darkness.
Takanuva was capable of illuminating the Zone of Darkness.
The Zone of Darkness was a pocket dimension.
The Zone of Darkness was a pocket dimension attached to the real world, not a parallel to the real world.
The Zone of Darkness wasn't a parallel dimension, a specific location in the dimension didn't correspond to a specific location in the main universe.
The Zone of Darkness was a pocket dimension, meaning it couldn't survive without the universe it was attached to. It was created by the Great Beings.
Unlike Karzahni's shadow tunnel, the Zone of Shadows didn't feed on light. Light simply didn't function in the dimension because natural laws there were different from those in the main universe.
The ground in the Zone of Darkness was likely stone. There was no need for dirt because nothing could grow there.
The ground in the Zone of Darkness was likely flat.
The Zone of Darkness was huge, large enough for Tahtorak and the Zivon to get space away from each other.
Each alternate universe had its own independent instance of the Zone of Darkness pocket dimension.