The blue room on dm_killbox_damien_final is accessed by running into the wall on the walkway to the left of the green snipers box. To get up there you can use one of the elevator pads located on the map (1), and jump as you start to ascend so that you vault up high in to the air (2) and land on one of the walk ways. Depending on which walkway you end up on you might need to jump across by using the stepping stones. Once you’re on the walkway left of the sniper box (3) run towards the wall until you enter the blueroom. (4)