Najd — the Great Desert

One horizontal world: Moon City west, Sun City east, the Cave at the centre. Biomes shift across it; danger rises inward.

The desert reads as one unbroken gradient, west to east: the black volcanic wastes of the Dark, through rock, mesa and open sand at the scarred middle, into the green steppe and lush river gardens of the Light. Roads and bridges thread it; two rivers wall the factions apart.