I completed all the pre-requisites (bunker key, blow up the wooden barrels, etc.), entered the wall at the arrow, searched EVERYWHERE INSIDE the wall, every square, every quadrant. Left and walked back in 5-6X and still no chest key. It's not there. Can someone help?
Items often only appear after you have taken certain steps in a specific order given you by the Oracle.
If you play the game out of sequence sometimes things, which you need to appear, never appear and you have to restart chapter from the beginning. Golden rule: Let the Oracle direct the main flow of play and only use clues given by non-playable characters subordinately.
Although NLT Media says that players can complete quests and tasks in any order they choose, in my experience this can go wrong, and the sure fire way to succeed is to do what the Oracle says in the order which the Oracle says it.
If something that should be there is not there in the game you probably will have to restart that chapter and replay it in a different order.
To navigate the path inside the wall: Make MC face the wall with the arrow in front of him; press the RIGHT cursor key and hold down for some seconds to make the MC walk as far as possible into the wall; press the UP cursor key for some seconds to go up as far as possible; press the LEFT cursor key for some seconds to go left as far as possible and and you should find the key.