The blue room in dm_killbox_enigma_final is accessed by jumping up in to the hole in the bottom of the glass room, which is attached to the middle of the ceiling. To get up there, you can use the teleports on the ground floor - either the square tile (1) or the center alcove in the bunker to the side of the room (2). From there you can run up the ramps to the 3rd floor (3) and then jump up in to the hole (4) which will teleport you to the blue room.