Panic House is a small dungeon that can sometimes appear in Westmarch Heights in Act V of Diablo III. It contains an unmarked event. It has two locked doors, behind which Westmarch soldiers are hiding. Letting them out will cause them all to become possessed, though, and turn to Revenant Archers, Revenant Soldiers and Revenant Shield Guards. It's not necessary to kill them all (especially considering they are getting reinforcements). The Resplendent Chest behind the right upper door is a reward for the player's trouble.