Note: An overshield with you is required. After opening the door where the Gold Elite with the plasma sword is located, make a right. There should be an intermission sequence where Master Chief kicks a rock to see how deep the fall is. This is what you are trying to do, except land at a certain place. After the intermission sequence, look to the right and down. Notice that there are two platforms at the right. Position yourself and jump for the second platform, then look below. The third platform should be underneath. Look for any walls that you can slide so that you will not lose any life or shields. Slide down and go all the way to the left. You should see the Silent Cartographer and Convenant guarding at the other side. Avoid alerting them. Sneak to the objective, press E, and you are done. Note: You will face Convenant when you must go back to the surface. If you have an overshield, your health will probably be at four bars and your overshield will be gone.