In Game Description
Key to the annex in the
Painted World of Ariamis.
In the wintery painted world,
there is a structure resembling an
old cathedral; its annex serves
as a type of storehouse.
Behind an illusory wall in the sewers/tunnels in the Painted World of Ariamis. These are accessed via the well in the courtyard with the Phalanx. The solid looking section of wall around the left of the first turn is the one to look for.
Alternatively, destroy the wall to the left of the switch in the large sewer area (with the Skeleton Wheels). Turn right, past the illusory wall, then left. You will encounter another Skeleton Wheel. The key is the item at the end of this corridor.
The storage annex in the Painted World of Ariamis