Turn right and head into the tunnel. Kill the raptor and make your way to the far end.
Making sure the tyrannosaur isn't nearby, drop down and jump into the small pool to the right. Surface on
the other side and kill the raptor. Now get the cog as you normally would and go back the way you came.
Now you should be surfaced at the small pool you just jumped into. If the tyrannosaur is lingering right there, go back and to the other end of the tunnel. Either way, the next part is the most difficult.
Start running to the temple. The tyrannosaur will probably notice you, but you're just as fast. Kill the raptors while running -- there's no time for stopping. Run into the temple and get the second cog.
Now look outside and to your right you'll see a ledge you can vault onto. Do so and enter the tunnel. This
will lead you to the broken bridge. Jump across and get the third cog.
The tyrannosaur is probably right below you. Regardless, you have to exit the valley, so safe-drop (or jump and take damage if you're nervous) and make a mad dash back to where you came from.
GAME BOOMERS hints, cheats, and walkthroughs