The underworld is another face of heroshi beneath the ground and can be accessed from almost anywhere. It is inhabited by dwarves, gnomes, goblins, deathshrouds, 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), molds, and mosses. As a place of chaos, the underworld is prone to sudden changes of layout. Some areas seep through into other planes and are, as a result, aligned or possess elemental traits that defy normal geology. In such areas, the inhabitants may behave in an entirely different manner than normal.

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.

Nethergrove

An extensive subterranean forest home to nether elves, who make their homes in the giant polypores attached to the colossal trunks of the trees. The subterranean canopy actually supports the ceiling of the Nethergrove's cavern. The city of Tenebral is the nether elf capitol.