I think you miss the one that under the 4 towers, I mean you have to go down one level first then find an elevator then go up then prepare for a battle (btw becareful with the traps around the elevator) then you will see a door in the middle (like a big tree) then you enter that door then prepare for battle again, in the last battle you will find the one broken machinery in the box.
sorry if my english is not good enough
