Source: The Witch Queen's Revenge, pg(s). 73
The Thrice-Tenth Kingdom is a wide plain dotted with dark forests at the foot of the Starcatcher Mountains. Below the earth are vast caverns echoing with the screams and moans of Baba Yaga's victims. In the deepest part of the deepest forest lies the Witchspire, a silver-and-glass castle built by Baba Yaga's minions from a thousand worlds in honour of her. The throne in its central chamber sits empty, as Baba Yaga never asked for this palace and usually stays in her Dancing Hut whenever she is present.
After Baba Yaga began her exploration of the Great Beyond, she wanted a realm that could be sculpted as she wished, and decided to establish it in the First World, due to its mutability to those with sufficient power. At the age of more than 500, she staked her claim and stabilised the Thrice-Tenth Kingdom, calling it to order in an idyllic image of the Russian steppe.
Strange fey inhabit the dark woods of the Thrice-Tenth Kingdom, hunted by inky black beasts if they fail to seek shelter at night. Between the mountains, weird ogres wage war. Elk and deer herds roam the steppes, seeking enlightenment. Talking birds bicker with each other, and even wriggling worms have their say, for the idyllic-looking surface hides sinister truths.