The Bastille of Intellect in Northern Pandora's Bane is marked as 'Complete' despite me never encountering it before. To access it, I had to break a wooden door, and entering the area all of the stone walls covering the music pylons were untouched. However, no music is being emitted, and the Essence basin is still glowing blue (but appears empty).
The Main Quest of Nightingale City has been completed, if that is relevant.
