I just found this, not sure whether this is accurate as I am/was stuck.
https://www.reddit.com/r/BaldursGat...s_the_second_path_to_the_moonrise_tower/During my playthrough I went to all the possible leads to a cure, and also found Halsin. However, I killed him and got the information as to Moonrise Towers from his body (speak to dead spell). This triggered the quest to travel to Moonrise Towers.
That was my final lead. Supposedly there is a road through the Underdark to Moonrise Towers, however, I have no lead to go there. There's a signpost in the Northwest area where the Gith are that say Moonrise Towers to the West.
However, you cannot access that mountain pass, despite this being the only lead you (like me) may have. So you go there, and nothing, at least at this point of EA. Without googling, I would be stumped.
