[Bungleau]

You can check one of Xignal's maps, but IIRC, from the cistern room you can simply go far right or left back to the main entrance. Go through the wing gate door in the middle, and that will take you to the lich. And if you haven't done so already, take a right before you get to the lich's room and flip the wing lever to stabilize the walkway. You'll appreciate it later (if not sooner).

And if you're that loaded up, be sure to head to town to empty things before you give the relic to the lich. He's going to give you something you'll want to carry... badly...