As for the prison itself, it wasn't located inside that gray land, but in another land that looked like an exact copy of the great world he just conquered.
The two lands looked identical to each other, facing each other and forming the ground and skies of each land. Arthur felt like passing through a separate membrane, separating two dimensions from each other.
Yes, this prison world was situated in another dimension, a dimension where the lands he previously conquered were barren and destroyed, with no speck of life appearing as far as he could see.
As for the other land standing above his head, suspending miraculously like it defied gravity, it was filled with a strange mist that covered up what lay deep inside it.
"Gege, can you scan that land?" Arthur didn't hurry to move as he calmly asked. First he got to know his current circumstances, not blindly charging inside his enemy trap.