So I posted some ideas here.
I changed the name to Crystal Temple to get away from the word 'dungeon' as I think the story seems to be leaning away from creating a 'dungeon', although that option certainly exists. I pulled in the ideas I've posted here, and updated the backstory wiki to add another event.
Note that I deliberately have not specified what the mystic part of The Shattering Dark was because I think that could be an interesting thing for the single player campaign (or one of them at least) could explore.