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This is on the level "The Ark." After you kill the Scarab, go into the structure in the middle of the sand (before entering the building) and pick up a grav lift. Head up the ramp into the building on the right. After leaving a room with a fair number of fusion cores, you will go down a narrow ramp. Deploy the grav lift 3/4 of the way down the ramp and walk into it. If done correctly, you should be able to launch yourself onto one of the higher "shelves" at the bottom of the ramp where the skull is located. If you are unsuccessful by the time the grav lift is exhausted, kill yourself, go back to the last checkpoint and try again. Difficulty: Medium