"The Den" is a very straightforward name, a hole in the earth.
Above the Floating Land lies the Celestial Sky, below it, the Dark Heaven.
The Celestial Sky hangs high above, visible everywhere. Dark Heaven lies deep and obscure below, blocked by the vast and boundless earth, essentially unseen.
But the Den is an exception.
No one can clearly explain how the Den came to be, only that it connects to the Dark Heaven. All tribes of the entire Floating Land must face the dangers that come from the Dark Heaven.
There is a legend in the Floating Land that above the Celestial Sky, there were many stars. They fell from the Celestial Sky into the Dark Heaven, piercing through the earth in the process, thus forming the Den. And ever since the fall of the stars, only the Heavenly Pivot star remained above the Celestial Sky.
Back to the Den. The dangers coming from the Dark Heaven are very specific and are not illusory.
