Nothing
The Void is a realm of nothing. There is no life, no color, and no traveling.
The Void was created at the ultimate confrontation between The Founder and The Ruin, who was readying himself to enter The Founder’s Realms. With the help of Maximillian Regalia, The Ruin was held in Black Haven long enough for the Founder to tear out a piece of his own soul and form it into a barrier over the tear in reality between Black Haven and The Edge.
It was this that made The Founder weaker, and vulnerable- forcing him to think more about the transference of his powers to his heir. The creation of The Void serves as the completion of The Founder’s character arc, and allows for him to finally become the benevolent ruler we see at the beginning of the novel.
“I looked through the sliver in space- peering into his eyes one final time. ‘My name is no longer The Creator- I too have become something new, it took me until now to understand what it truly meant. You may remember me forever as, The Founder.’”