The decision to send a manned expedition into the obsidian hallway was not made lightly. While the Bone-Clapper had mapped the first hundred yards, the crystal map on the pedestal suggested a journey of dozens of miles before the first potential "Surface-Vent" appeared beyond the Imperial blockade. Kael could not risk the elite of the Metrology Guild on a whim, but the "Golden Finger" warning was a persistent, low-grade hum that wouldn't subside. It was a signal of opportunity, a window that would not stay open forever as the mountain's internal resources continued to tighten under the seal.
The technical core of the expedition was the Sled-Base. This was a low-profile transport vehicle constructed entirely from non-reactive materials: a frame of seasoned oak, runners of polished whalebone, and a propulsion system based on a massive, hand-wound torsion spring. To minimize the thermal and acoustic signature of four men, Kael engineered "Acoustic-Shrouds"—heavy, multi-layered cloaks made of peat-fiber and treated flax that acted as portable sound-dampeners. Each man was equipped with a "Lung-Box," a small, charcoal-filtered rebreather that scrubbed the moisture and scent from their breath, preventing the ancient sensors from detecting their biological presence.
The grit of the journey was the absolute sensory deprivation. To avoid triggering the light-sensitive "Static-Lumen" cornices, the team—consisting of Kael, Silas, and two senior scouts—traveled in near-total darkness. They used "Tactical-Touch" rods, long sticks of bone tipped with soft felt, to feel the edges of the hexagonal walls. Every movement was slow and deliberate. They didn't walk; they glided on the sled, the only sound being the faint, rhythmic click of the torsion spring unwinding. The air grew colder the further they moved from the geothermal bore, a dry, crystalline chill that made every joint ache.
Socially, the departure of the Baron into the "High-Toxicity Zone" created a vacuum of authority in the lower tiers. Elms was left to manage the thousand souls of Ashfall, a task that required him to balance the dwindling Green Ring harvests with the increasing demands of the Protein Vats. The grit of leadership without Kael's presence was a heavy burden; the citizens were restless, their ears tuned to the iron pipes, listening for any sign of what lay beneath Tier 17. The secrecy was a thinning veil, and the fear of the unknown began to manifest as a series of small, uncoordinated strikes among the Tier 0 laborers.
The physical reality of the trek was a grueling endurance test. By the tenth mile, the obsidian hallway began to widen, the hexagonal symmetry giving way to a vast, vaulted space that the bone-whiskers could no longer reach. The "Golden Finger" in Kael's head suddenly shifted from a hum to a sharp, rhythmic pulsing.
"Stop the sled," Kael whispered into his rebreather, the sound muffled and mechanical.
He didn't need light to know they had reached a "Sentinel-Gate." He could feel the change in the air pressure—a localized pocket of high-density air that acted as a physical barrier. This was a "Pneumatic-Lock," an ancient system designed to keep different sectors of the deep-road atmospherically isolated. If they pushed through without equalizing the pressure, the sudden rush of air would trigger every acoustic alarm in the sector.
Kael utilized the "Syringe-Equalization" method. He had brought a series of hollow bone needles connected to small, hand-pumped bellows. He carefully inserted a needle into the invisible "wall" of the pressure-lock and began to manually bleed the mountain's air into the ancient vault. It was a painstaking process that took six hours of constant, rhythmic pumping, each stroke of the bellows a gamble against a sudden rupture.
A technical failure occurred as the pressure finally leveled out. The ancient "Lock-Mechanism," sensing the return of atmospheric equilibrium, attempted to cycle the gate. But the gears, made of a bronze-like alloy, had suffered from "Cold-Welding" over the millennia. Instead of sliding open, the gate shuddered, a high-pitched metallic screech echoing through the obsidian hall.
The internal warning in Kael's head flared into a roar.
"Brace for a kinetic discharge!" Kael signaled, pulling the scouts toward the floor.
From the ceiling of the vault, a series of "Guardian-Spheres"—small, polished obsidian orbs suspended on magnetic tethers—began to drop. These were not explosive; they were "Vibration-Seekers." They functioned by homing in on the specific frequency of a beating human heart. As the spheres began to hum, Kael realized that their "Acoustic-Shrouds" were insufficient against such a direct, localized scan.
Kael utilized the "Heart-Masking" technique. He ordered the scouts to press their chests directly against the cold obsidian floor. The polished stone, with its massive density and sub-zero temperature, acted as a "Heat-Sink" and a "Sound-Baffle," absorbing the vibration of their hearts and dissipating it into the bedrock. The Guardian-Spheres circled for ten agonizing minutes, their violet sensors sweeping the air inches above the men's heads, before the lack of a biological signal caused them to retract back into the ceiling.
The engineering of the "Sentinel-Gate" was eventually bypassed as the gears finally broke free and the massive obsidian slab slid into the floor. Beyond the gate, the hallway didn't continue; it opened into a sprawling, subterranean chasm.
Kael stood at the edge of the ledge, his lantern dimmed to a mere sliver. Even in the gloom, he could see the outlines of a city. It wasn't built of stone and mortar, but of light and geometry. Massive obsidian towers rose from the darkness, their surfaces etched with the same violet patterns as the hallway. There were no people, no movement, and no sound, but the city was alive. A low-frequency hum, deeper and more powerful than the mountain's geothermal bore, vibrated through the floor.
"It's an 'Automated-Polis'," Kael whispered, the "Golden Finger" finally settling into a steady, calm glow. "A city that operates without a single living soul. And look at the ceiling, Elms—if you were here, you'd see it."
Far above the towers, a series of small, natural fissures in the cave roof revealed a faint, flickering light. It wasn't the sun, and it wasn't the arc-lamps. It was the "Starlight" of the southern wastes, filtered through miles of rock. They had found an exit, but it was at the heart of a machine-city that had been waiting for a visitor for ten thousand years.
The population count in Ashfall remained at 1,000, but the world had just become infinitely larger.
"We can't bring a thousand people here yet," Kael told Silas, his eyes fixed on the distant starlight. "This city is a 'Clockwork-Labyrinth.' We have to learn its language before we try to walk its streets. But the road is open. We have a way out of the Empire's shadow."
Kael began sketching the Sector-Map, a detailed grid of the automated city's primary thoroughfares, marking the positions of the Guardian-Spheres and the pressure-locks they would have to master to reach the surface.