The Word That Returns

You enter a long stone hall whose ceiling disappears into darkness. Every footstep returns a heartbeat later from somewhere behind you, followed by a softer repetition from the walls. At the far end stands a sealed door of black granite, its surface carved with listening dwarves. Before it rests a mouth-shaped pedestal and a bronze floor plate. Thin silver channels connect both to the door, pulsing faintly whenever anyone speaks.