Crux of nothingness hideout

Well hello everyone!
I have been looking for this as a hideout, the arena were you fight ”the king of the mist” but i cant find it.

Have anyone seen anything like it?

I also saw it in a recent post that GGG made i the news feed, when they showcase the crux portal effect, you can see the crux of nothingness arena.

Thnx for the help.