How to get the yellow key in level 8, FINAL OUTPOST:

The yellow key sits on a short pedestal in a small room.
Inside the room, to either side of the door, are switches
in the corners that raise and lower a cage around the
yellow key.
If the cage is down around the key, raise it.

From inside the room, open the door and look straight down
the short hallway ahead.  About halfway down that passage
you'll see a brightly lit area.  Step into that lit area
and look for a square panel in the wall on the right.
Activate this panel like a switch, and the pedestal where
the yellow key sits will drop down, allowing access.

Hope this helps. :)                                      

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