Underworld
The Underworld is the realm beneath the earth, divided into nine levels including Subterranea.
First named in The Yellow Knight of Oz, ch. 7
The Underworld is divided into nine levels.
Where this is
placed Beyond the desert worked out
read out of the chapters cited on this page, not stated in any one sentence of them
Reached from beneath Speedy's real-world Long Island home, a fantastical realm parallel to Oz rather than inside it or literal Earth geography.
What the books say it is
size divided into nine levels 1 chapter
And clutching Speedy's arm, Zunda began to drone out like a schoolboy reciting a lesson: "The Underworld is divided into nine levels.
The Yellow Knight of Oz, ch. 7