Two Weird Fantasy Megadungeon Ideas

Old Jerah: Once the City of Mot, the One Who Pulls into His Gullet, now all that is left of Old Jerah are broken buildings and its supposedly endless catacombs.  When the priest-kings of Jerah ruledit was known as a place of great terror, and all slaves and soldiers feared becoming the next sacrifice to the Black God of Ghouls.

Then, if accounts are to be believed, the demon Li-Lit appeared in the temple of Mot and slew his priests and the Priest-King himself.  Only the women of Old Jerah, which was famous for it's misogyny even among the harem managers of Almodad, survived.  They fled the ruins and founded the city that men currently call Jerah and set there a black temple dedicated to the night demon that freed them.

Since then Old Jerah has lain in ruins.  The merchants who travel in caravans that pass near the outskirts of the necropolis tell dark tales in the taverns.  They whisper of inbred degenerates, hyena-headed ghoul-priests, and strange lights that dart about the ruins.



The Hell-Caverns: In the eons before humankind walked the earth far stranger races built towered cities on the great continents of the world.  Great were the heights they reached, and even greater were the cataclysms that crushed their palaces beneath the earth.  Many were their names and numbers, but all these are lost to humankind's memory.  Their forms too were numerous, and they can be guessed at from their degenerate descendants that often dwell in the deep places of the world.

One such place lies near a small town in the Languedoc region of France.  The rocky landscape hides a vast network of caves and ruins.  Many of these ruins were built by humans in some forgotten epoch when fair Atlantis or distant Mu were in their infancy.  Some are older still, built by slithering things with alien masters.  These creatures wielded magic and technology beyond the understanding of men.

Those that have gone in the caves seldom speak of their experiences.  Those that do often are cleansed with holy fire by the Church, for what they say questions the nature of humankind and its centrality to God's universe.  Some even question the existence of God, pointing to the unquiet things that lurk in the dark as evidence that some far more strange power than Him governs the universe.  Those that can be bothered to stop their heretical babbling do tell of glittering gems and items of wondrous power, but their usually shuffle off this mortal coil shortly thereafter.