For better or for worse, the visual that inspired this image has been in my head for more than a decade: a huge, vertically stacked dungeon region, dominated by the massive circular structure created by a cabal of aloof wizards.
Now I finally know what's there!
The Cleft of Five Worlds is an adventure region. Rather than a specific, detailed adventure, it describes a bunch of adventure sites and settlements in relation to one another.
I will revisit it to flesh out its parts in later months, but the enterprising among you will have no trouble stocking it or ripping out bits you want to use elsewhere in the meantime!