It was dark in the Abyss.
The concept of light was drowned in the blackness. It existed, but it didn't exist in its full form. There was a brightness that allowed one to see the path ahead, but there was no path ahead to see.
Unless one had lived here for enough time to become accustomed or was born here and knew nothing else, its scenery alone was suffocating enough to drive one to insanity.
However, to the Nox, this was home.
The Abyss was always perceived by those in Grand Heavens Boundary as a vast emptiness, but this definition was flawed.
The majority of the Abyss was created after the destruction of universes, the tiny trace of the blackness that existed in the past devoured and grew into its current form.
Therefore, while there was only a single complete structure in this place, Al'Katra, it was scattered with debris from those previously existing universes.