Mulcarn, Angel of Winter
The vault is dominated by a great mountain. The mountain is larger than any on Erebus, it is steep, rigid and punishing. The pinnacle is called the throne of hell (not an actual throne) and is the main gateway between the hells and Erebus (in the Fane of Lessers) and the portal through which souls are drawn into hell.
The mountain gets colder the higher you climb, and its base and rocky spires are hunted by the remaining servants of Mulcarn, frost giants, frostlings, aquilan and the nive.
Below a vast waste slopes away from the mountain. The rough tundra turns into a swamp. Each step through the swamp is a battle and the languid pools pull at anyone trying to get through them. Beneath the surface the largest source of petitioners in hell are trapped, this is the purgatory for the non-committal. They lay here for ages, consuming their own excrement and feeling nothing but slight pain and lethargy. In time they will overcome their passive nature and continue down into hell, but for now they are victims of their own inaction. Tar demons are pulled from these pools, gelatinous blobs with little humanity remaining.
There are creatures in the swamp, mites and bugs that leave horrid burning blisters where they bite. They are not deadly, most that travel here are immortal, but the creatures steal the strength of those that pass through the swamp, inviting petitioners to lay beneath the black waters and succumb to the mindless eternity that this realm offers.