After entering the Reliquary in the Academy , turn right on the first fork and once again on the other side of the stone bridge. If you come across any locked doors, come here again once you complete all missions for the librarian .
Behind the stone gate you will find a room filled with bookshelves . Above one of them there is a yellow sphere . Shoot it with a ranged weapon and it will change its location and/or colour. Attack the red ones with magic, blue with melee weapons and yellow with a rifle.
After a few shots the door will open . Behind it you will find stairs leading to a next sphere .
Hit it, jump down  and repeat the process .
Once you get rid of all the skeletons, a platform with a blue arrow will appear by the passage . Step onto the shining triangles and you will successively create stairs which will lead you to the Golden Door .