Found something else, inside the Grove in the antechamber where Khaga and the black druid hangs out.


There are interactable plaques with writing around pillars that explain the painting on the walls showing how the Grove was created. One of the section of the room has collapsed pillars hiding the wall behind, but the plaque is still there. That one talks about the druids fighting Shar followers and the Moonrise tower. The narrator link the Moonrise to Selûne (no check required or anything).

So the Cult of the Absolute HQ is inside another Selûne related building.