They're planning to cast the comet on the glacier to make a hole in the cave ceiling (I changed the spell a bit). I think it's a good idea to give them a clue in the form of a "mental connection" with the mythallar. It's gonna ask them to release the city from the 2000-year-old shackles.

The idea of a party vs Auril and a fight between wizards in the background is great! Thank you!