Jon is about to shrug when the eye that makes up the floor of this place closes, the different reflections vanishing as this happens and the room is left cast in absolute darkness. Only the light glow of Jon's own eyes remains. It's hardly enough to illuminate the room, but once Gladio's eyes adjust to the darkness, he may be able to make out the outline of a rectangle on the floor at the center of the room, glowing the very same shade of green as Jon's eyes. And if Gladio feels inclined to investigate the rectangle, he will figure out that it's a trapdoor opening up to a long staircase circling its way down, illuminated in dull, faintly pulsing green light.

"Ah." Jon says, understanding. "I- I suppose that answers that question."