A Resonance in the Tiles

The concrete ramp led downward into cool, shadowed air. At the bottom, a curved tile passage stretched out without a soul in sight. I halted near the middle, where the arch curved overhead, and stepped lightly on a loose drain cover. A clean metallic ring bounced from wall to wall, lingering long after my boot lifted. I tested a single low hum into my microphone grille. The tiled curvature amplified the frequency into a deep, vibrating drone. Perfect acoustics exist in the strangest municipal tunnels.