From the 9 door hallway, enter the courtyard.
You will see a path ahead of you and a path to the right.
Ahead of you, see the first letter panel; enter CA.
At the middle of that path, enter AC on the letter panel.
At the end of that path, enter DB.
Now turn to the right path.
To your right is the first letter panel. Enter BD.
At the middle of that path, enter BA on the letter panel.
At the end of this path, enter DC.
Now turn to the right and you will be on another path (bottom part of the enclosure).
To your right is the first letter panel. Enter AB.
Beside this letter panel is the button stand.
At the middle of that path, enter CB on the letter panel.
At the end of this path, enter DA.
Turn the right at the last path.
To your right is the first letter panel. Enter AD.
At the middle of that path, enter CD on the letter panel.
At the end of this path, enter BC.
Now go back to the button stand close to the letter panel that you changed to AB.
Press the button and the center hill will light up.

North
CA ---- AC ---- DB
BC -------------------- BD
CD -------------------- BA
AD ------------------- DC
DA ---- CB ---- AB