Thunder Under Needlespire - Dungeon Magazine 24

Ok, Ptolus DMs, do you want an apocalyptic battle against a very powerful Galchut deep below the Spire?

OF COURSE YOU DO!

Thunder Under Needlespire just might be that adventure. The name is coincidental, but maybe it's an omen that this needs to be reworked to match your preferred game edition and run as a possible campaign turning point. In the original write-up the AD&D levels are for 8 to 12 with the main villain being 20HD and you'll be ambushed by a Drow wizard and a summoned demon at the same time you encounter the thing.

Screaming to be adapted into a higher level fracus, the module takes place deep in the caverns where Svirfneblin (deep gnomes) approach the characters for help with what the gnomes believe is a few Illithid causing earthquakes. It turns out the Illithid want help with the real cause of the problem, a Galchut about to break free of a cyst and in the process destroying vast areas and civilizations beneath Ptolus. Oh, it would also wreck the city and maybe topple the spire.

Characters begin thinking it's a few mind flayers and a handful of their servants to take care of and end up discovering an Illithid outpost with 3 dozen of them, plus dozens of servants, a Drow advisor, and a Beholder ally. The potential for an "oh, shit" moment exists when finding yourself surrounded by a bunch of brain eaters and a beholder.

Fortunately the tentacle-faced creeps don't want a fight, they want someone to accomplish what they are unable to do which is to destroy the thing causing the earthquakes. They know what is at stake. The Galchut is immune or extremely resistant to their mental powers, reflecting their attacks back at the Illithid. They need muscle of the type the party can bring to bear.

On the way to fight the big bad monster the party gets followed by a Drow out to make a name for herself. She too knows what's at stake and thinks by making sure it happens she'll earn a place at Gorgoth-Lol's (Lolth) side. When the party enters the lair of the Galchut, she summons a demon and attacks the party. (In the Ptolus setting Gorgoth-Lol is one of the Vested of the Galchut)

After the party defeats her, the demon, and then the big bad monster (assuming they manage to do so), their guide sent by the Illithid, surprise attacks them per her master's orders. She's a wererat wizard supplementing her own magic with some powerful scrolls she's saving to unleash on the party.

You could certainly expand this into a longer, more involved mini-campaign. Other under-dark, under-deep, whatever you call it, races could play a part along the way.

There's a lot of conversion work to make it ready to play, but Thunder Under Needlespire might be worth the effort.