I'm in search of a good module or part of an AP that can be used as the demiplane workshop/laboratory of a crazed summoner/elementalist (oriental 5-element type). Even pointers to bits and pieces that I can kludge together will be appreciated.
As a sidequest for two of the characters in the Age of Worms game I'm running, they helped clear out an old dwarven stronghold that had been taken over by an immortal summoner. Backstory is that the guy couldn't be killed, so they stuck a wounding sword in him and just sealed him up in walls of stone forever. However, some hundreds of years down the line, a group of miners thought the legend was just that, and accidentally woke him up (understandably mad in both senses of the word). Guy starts summoning various elementals (refluffed golems) and wrecking the city, forcing the dwarves out.
Long story short, they killed him (discovered his weakness and exploited it) and found a strange glowing crystal in his belongings. My (vague) idea was basically that it was the "tuning fork" for a demiplane he'd created long ago. Well, the group's caster just got plane shift, so they want to follow up on the storyline.
I have a few treasure and creature ideas for what they'll find, but I've been spending most of my creative energy trying to write up the Test of the Starstone for another character in this group (much later down the line, say 17-19th), and they caught me slightly off guard wanting to go investigate now.
Are there any good modules around level 12-16 (or higher, I can tune things down to fit the characters) that have this sort of theme, or something that could be refluffed to fit?