When you reach the light bridge, it is possible to get to the bottom
of that area by using a warthog.When you enter the room, on the left side
there should be a small part of the floor which reaches out. It should have
a glass floor. Use the warthog to jump off here, then try and slide down the
wall on the other side to slow you down. This is quite hard to do so it will
take a few tries.