The Wilderlands of High Weirdness
Dungeons and Hell
Hell is the Underdark turned up to 11. It’s the mythical underworld. Hell is where people go when they die. Monsters come from Hell. Not every dungeon or other underground location is in Hell or leads to Hell, otherwise the Wilderlands wouldn’t have a single root cellar or underground sewer, but going underground is never an act that does not carry risk of a Hellish encounter.
Hell gets weirder the deeper you go. The natural laws change slightly, in ways that make it hard to leave. Time and space feel distorted, making it easy to get lost. Doors become hard to open, but won’t stay closed for you against your pursuers. Sources of light get dimmer, as if the surrounding darkness consumes and thrives on light. Where inhabitants of the upper tunnels are of familiar, if degenerate, peoples, the deeper denizens of Hell are more distorted, if not altogether alien.