Hell
Despite its reputation as a scalding hot cauldron of magma & fire; Hell appears to be... quite the opposite. An endlessly twisting cavern, covered in snow, ice, and frost; Hell is a dark, frozen wasteland with little light. It was once populated by True Demons; otherwise known as Fallen Angels, long ago; but they've all reincarnated as humans & presumably died out, by now.
What remains are the Hellbound (e.g; Atlas), spirits of dead humans, who, for whatever reason or another, didn't qualify for entry into Heaven, and now await the day their time in Hell is over & they can reincarnate. Usually lasting only a few years at most; nobody quite sticks around Hell for too long. Their appearances tend to be more demonic; resembling furry animals with red details & a proficiency for fire.
Unbeknownst & forgotten to all, contrary to what quite literally everybody believes; Hell wasn't originally supposed to be a place of punishment or torture, or even misery. It was simply a place for souls to rest, recuperate, and reflect, until they were ready to begin life on Earth anew. Even the Hellbounds' demonic appearances reflect this- their beastly forms aren't punishments; their souls manifested with the forms needed to best handle Hell's current frigid environment; if Hell were warmer & more Earth-like, Hellbound would look much more human.
A beacon of darkness; originally planted there by Fallen Angels, lies at the heart of these endless, twisting caverns; covering the entire realm with a shadowy smog, blocking all light & warmth from entering.