Leaving the freezing glass beds of the discharge quarry, the passage climbed through a steep andesite stairs into Entry hall 702: The Gallery of the Resonant Flues. Here, the heat normalized back to the cool stone baseline of the deep halls. But the air was filled with an extraordinary sound phenomenon that arrested them both upon the threshold.
The hall was a long, narrow gallery sixty arm-lengths long and ten arm-lengths wide, flanked on both sides by massive upright pipes of rolled sheet copper three paces in width. These pipes were the main exhaust chimney pipes of the underground air-flow system. It rose through two hundred deep-water lengths of solid rock to the ancient sea-level intake towers above.
From within these copper chimney pipes, a nonstop, mournful sound was rising. A low, melodic wail that fluctuated between twenty and twenty-six hertz, producing a sound undulation that rang directly in the hollow chambers of the throat and chest. It wasn’t a clockwork roar or the whistling of a draft. It was a slow, rhythmic lamentation, rising and falling with the rhythm of human grief.
Qiao Ming stopped in the center of the gallery, his bare horn-hard feet gripping the flat stone slabs. He tilted his head, closing his slate-grey eyes to listen with the refined sound senses of a deep-sea land-mapper. He listened to the pitch, the ringing intervals, and the load-bearing dampening of the wave.
