Finding this terminal won't help unlock the Achievement, but it will reveal a new Cortana cutscene with extra dialogue. For fans of the Halo novels, there's even a hidden reference to Ghosts of Onyx.
To access the optional terminal, run through the Cortana mission until you drop through an open hole in the floor (a hole not covered by the one of the level's nasty sphincter doors). If you've already nabbed thegold skull "Tilt"using ourSkull Video Guide, you'll recognize the right room.
Head out onto the circular platform and look down. Through the glass floor, you'll see the area you need to get to. Simply drop off the edge and walk underneath. The terminal glows white in the back.
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