The landscape of this world is nothing but a barren wasteland or never ending white sand with huge dunes. (It somewhat resembles the Shinigami Realm in Death Note) The dessert is littered with boulders and dead trees but these are actually in the form of the rock; Quartz. This world is in constant night and the moon is in the opposite lunar phase as the one in the Human world. Like Soul Society, Hueco Mundo's atmosphere comprises of Reiryoku which forms Reishi, but the
Hueco Mundo is a world located between that of Soul Society and the Human World, though is separate from another world known as Dangai. The only way to access and enter it is to rip the fabric separating the worlds from one another, something only Hollows and Shinigami are known to be able to do, the ripping of this fabric is what allows hollows to move from their world to others at will. Depending on the power level of a Hollow the effect of this rip varies. Regular (low level) Hollows will appear from a small, black vortex or out of a dark coloured smog whereas the Menos Level Hollow can be seen actually walking through the rip in the fabric. Arrancar use a more stable portal known as the Garganta.
The active life on the surface of Hueco Mundo is "few and far between" as most Hollows prefer to dwell under the surface unless otherwise provoked to leave their dwelling. It is said that all Hollows can live in Hueci Mundo despite shape, size, power, etc and in the anime it has been proven that Hollows can drag other souls into Hueco Mundo, one such case occurred with Orihime's brother, Sora Inoue who was forcefully made into a Hollow and sent to attack the likes of Ichigo Kurosaki.
However, although a barren and desolate wasteland it does, loosely, have some sort of Monarchy that lies within the Palace called Las Noches, which was formerly owned by Espada #3 Barragan Luisenbarn, King of Hueco Mundo. It is now, however, used as the Headquarters of Aizen's army of Arrancar.
Underneath the surface of Hueco Mundo is a forest, which was mentioned in the anime, it's extremely vast and is home to the Menos Level Hollow, the trees extend from the floor and poke out of the surface, dotting the landscape. All Adjuchas level hollow in this forest are under the control of Aizen.