Lead by the Espada. Las Noches is a massive fortress which can be seen for miles in Hueco Mundo. It consists of a main building with a domed center surrounded by several large towers and smaller buildings. They reside there with their army of Arrancar complete with medical facilites and detention wings. The Daylight Dome
The landscape of Hueco Mundo is a seemingly never-ending white desert, with dunes like those of the Sahara. The desert is littered with what appear to be boulders and shriveled trees, but these are actually a form of quartz.
There exists a vast forest underneath Hueco Mundo where Menos-class Hollows reside. The trees in this forest extend to the surface and dot the landscape above ground. The Adjuchas-class Menos which reside in this forest are under the control of the top 4 Espadas