Niflheim

The second layer of Hades is a vast pine forest stretching into infinity filled with thick curling mists. The trees have an unhealthy look to them largely because of their dull gray barks and thin needles. A chillness hangs in the air, which combined with the mist creates a moist feeling everywhere. The ground rises and swells in low hills marked only occasionally by a lone mountain, though lakes of dingy gray water are frequent across Niflheim.
The creatures that stalk through Niflheim are well adapted to the mists, which otherwise obscure vision beyond more than 60 feet. Creatures that rely on sight are going to have a hard time in the forests so the native monsters use other senses to track down their prey. The fearsome garmr, wolves of the mist, are completely blind and hunt by scent alone – their fearsome howl can unnerve even the bravest of foes. The foglet use the mist as their advantage, and can teleport through the thick fog.
The ambient light of the gray sky overhead is the only illumination on Niflheim; the mists seem to actively attack and swallow other sources of light brought into the pine forest. This suits the residents just fine

Geography

Death of Innocence

Squatting in the pine forest of Niflheim sits the isolated frontier town, Death of Innocence. The people that have drifted into its wooden-timbered buildings and muddy streets all share the viewpoint that death is the only release from suffering, but they are too selfish and too arrogant to die by their own hands. It is a grim town, with clawing mists as thick as anywhere on the layer hanging around it, but it does offer some respite for those lost to Niflheim’s heavy pine forests
What about the site attracts travelers and draws the ire of Hel? There have ben strange occurrences in Death of Innocence witnessed by travelers, including glowing lights, distant laughing voices, the tinkling of bells.

Finnvang Forest

Finnvang Forest is a stretch of pine woods in Niflheim that seem to the untrained eye as any other patch of foggy wilderness on the layer. It is the realm of Zulkaz the Troll King, and the legions of immortal trolls and ogres that live in the forest scour the region without end. Zulkaz’s forces have orders to bring any trespasser into Finnvang Forest to the Troll King’s dreary gray stone castle.

Features

Niflheim Clinging Mists

The gray pine forests of Niflheim are largely obscured by thick, grasping mists that envelop the entire layer. They curl around the trunks of the gray trees, between the tufts of gray pine needs clinging to the branches, and help hide the natural pits, lakes, and swamps that dot the layer. Anything more than 30 feet away is heavily obscured by the mists, and vision is completely blocked at a distance of 60 feet by the pine trees and mists.
The mists also resist attempts to disperse. A spell like gust of wind can swirl the mists for a short period of time, clearing an area, but as soon as the spell effect ends the fog rushes back in and reclaims what it lost. Some planar scholars claim an intelligence sits behind the mists, or a combination of the two, but few give credence to these ideas. And the mists certainly don’t respond to anything that would suggest a sentience behind its thick, flowing movements.