From where you begin the level, run up and to the right to find a lever you can pull...so pull it. This will raise one half of a stone bridge across the crevice. Run out onto the half-bridge and use Prince Caspian to shoot the lion-head-target-thing, which somehow magically raises the other half of the stone bridge.
Finish crossing the bridge, go left, chop down some vines and step on the pressure plate there, then head up the small ramp there and step on a second pressure plate. Two statues will rise ominously from the ground (scary!).
This fiendishly clever puzzle requires you to make the two statues turn and face each other, so....pull the lever next to each statue until they do.
Hold hands and skip through the door that opens to complete this mission and unlock your 10GS.