It is possible to get to both the top and bottom of Damnation. When walking out of the red base on the top, make a left and there is a pipe that runs from the platform to the wall. When on the pipe look straight down with a rocket, jump up, and then fire your rocket so that it propels you up. This can only really be done with a higher shield. Once you are up then jump on the pipes right in front of you then toss a frag grenade at the slanted wall in front of you and use the blast to propel you up onto another slanted platform. Then you can walk around the top of Damnation and you are able to see the whole level. Also in multiplayer, the pipes where you first blast yourself up is a good hiding spot when you have the flag.
To Get to the bottom, you have to stand on the bridge where the overshield is located. Then you have to throw a grenade at the off the platform, making sure that you get the overshield right before you hit the blue abyss. Your shield charges as you are falling, and the final result is standing on the bottom of the Damnation for a few seconds. This takes a really long time to get