The underworld is another face of heroshi beneath the ground and can be accessed from almost anywhere. It is inhabited by dwarves, gnomes, goblins, illithids, and many monstrous creatures. Tunnels are the roads of the underworld, winding under the surface at varying depths. The deepest tunnels even go under the ocean. On the surface there are many passages that lead through the underworld, but these are not tread lightly. Bodies of water appear in the underworld from steams to lakes and rivers to seas. Vegetation that thrives in the underworld includes fungi (mushrooms can grow to the size of overworld trees), mosses, and

Oinshelm

This dwarven capitol is built completely in the underworld, having only a few defensive structures built into the surface of the mountain and an airship dock at its crown. Below is a many leveled metropolis.

'Ald Fel

This dwarven ruin a.k.a. Vilhan's Folly is located in the mantle of The Serpent's Maw. Its top level is an observatory. 'Ald Fel continues through the crust of Heroshi and grazes the core.