Enter the production tower | Shutdown Halo 4 Guide

Enter the last tower. Inside you find a blue beam of light, which jumps you out on the higher level of this structure. When you get closer to the passage between constructions, the bridge will collapse. Before you enter the passage on right, kill as many enemies as you can.

Next passages will be very well protected, also by cannons. The most important is to eliminate enemies from the biggest possible distance, so they even can't start firing. Two ways lead to the target, but they don't differ.