Ah... My idea of time travel didn't make it...

Hey, good luck with developing it! I don't have any ideas for side quests but I hope this enterprise of yours succeeds!

Hey i just got another great idea.

Quest - The Shadow World

I've played NWN before, and i'm sure you can pull this off with some scripting. The quest begins with the character finding a book called "Principals of Planar Shifting", and this book has the unique ability, to warp your character to an alternate plane (such as the shadow world, etc). The character must use this book to switch between planes to complete the quest of defeating the shadow legion, that plans to use the book to invade the material plane.

maybe have a small peaceful town with this really dark looking castle like building that's just erupted out of the ground, and it looks really out of place,
and have it overtake one or 2 of the villages houses to make it look as though it's erupted into an awkward place

your quest is to investigate the building, and there could be a boss or something cool in there.
oh and the building can always be bigger on the inside :P

i'm trying really hard to be creative, but it just isn't happening xD
guess i'm too tired to think, it's 5am and i haven't slept yet :S