In the level Subconscious, there’s an area south east that you go to, to start a mission involving TK Baha. Just a little to the west of this area (almost at the edge) there’s a undiscovered misson in a seemingly unreachable area.
While I was playing earlier I noticed this too. I finished the story and all the other side quests in the area. This one just seemed to be in the middle of nothing.