The dwarven rifleman gives it away, and those are definitely Big Bad Pauldrons on the orc (I should know, my ret pally got stuck with a pair of those things for about 20 levels).
It is end of Hall of reflection dungeon , where in last phase of this dungeon you "run" from the Lich King , and must kill wave of his minions , and at the end of "running" you go through cave passage , where you got help from horde ship (in this case) which barricaded exit that Lich King can't go through .
