Acoustic Recon

Curiosity pulled me right past the elevator to the heavy steel stairwell door. With a firm nudge against the bottom edge, I slipped through into a concrete echo chamber! The painted yellow handrail looped down into dizzying depths, so I decided to run an acoustic test. I fished a shiny metal paperclip out of my glove, leaned over the landing threshold, and dropped it straight toward the lower step. The sharp 'ping-clack' echoed all the way up through the open shaft like a sonar pulse! Calculating the reverberation time, that's at least four full levels of uncharted vertical terrain waiting below.