They did not return to the surface immediately.
It would have been the prudent choice if Lin Yuan were thinking only as a man who had just survived a buried trap and destroyed a half-dead guardian. But prudence was only useful when it did not leave answers to rot within arm's reach. The broken construct lay where it had fallen, the seam in the rear wall open like an old wound, and the incomplete key fragment still hummed faintly from the force that had passed through it. Behind that newly opened gap waited a path no one else in the region had seen in generations.
Lin Yuan looked at Mu Qingxue. She met his gaze and gave a single short nod. Gu Tian, still breathing harder than he would have liked anyone to notice, clicked his tongue but did not argue. Mo Qian muttered something about how all terrible decisions began exactly like this. Bai Lian checked their wounds one last time. Su Wan stared into the darkness as if listening to a distant winter no one else could hear.
Then they passed through the breach.
The corridor beyond was unlike the one before it. The air felt older, denser, and strangely alive. The walls were not lined with decorative stonework but with channels that curved and branched like the walls of some buried artery. In several places mineral deposits had grown over them, yet a faint pulse still moved beneath the crust, weak but unmistakable.
Mu Qingxue lifted the lamp and exhaled slowly. "This isn't only architecture," she said. "It was built to carry something."
"Qi," Bai Lian whispered.
"Qi, yes," Gu Tian said. "But more than that. Transfer, pressure, support. This was part of a living formation body, not a single chamber. Our mountain sits on one vein of something much larger."
Mo Qian ran two fingers along one wall and held them up. Fine silver dust clung to his skin. "That is not what I wanted to hear while standing inside it."
Lin Yuan stepped forward first. The medallion lay hidden beneath his robes, but its reaction was growing harder to ignore. It did not burn. It did not shine. It simply answered the buried structure in a way that made every silent turning point feel personal. At the edge of his sight, the system flickered once more—resonance deepened, route node detected—and vanished before anyone could notice the slight narrowing of his eyes.
The tunnel descended in a gentle spiral. Twice they passed broken side passages that had collapsed long ago. Once they crossed a chamber whose floor had split open to reveal a chasm threaded with dead conduits. In another place they found fragments of wall paintings under soot and age: robed figures standing around pillars of light, mountains linked by lines that did not represent roads but something far more ambitious.
Mu Qingxue crouched beside one mural fragment and brushed away dust with her sleeve. "This iconography doesn't belong to frontier sects," she said. "And it doesn't match the surviving patterns of my clan either. It's older than both."
"Older is rarely comforting," Mo Qian said.
Gu Tian gave him a sideways look. "Wisdom at last."
They continued until the corridor widened into a circular chamber supported by twelve narrow columns. Half of them had collapsed. The others leaned under the weight of centuries. Yet in the center, rising from the floor into the ceiling, stood one intact pillar of black stone veined with pale light. It had been dark when they entered—but as the incomplete key fragment drew nearer, the light within it brightened.
Everyone stopped.
The pulse that came from the pillar was slow, heavy, and deliberate.
Lin Yuan felt it under his feet and in the medallion at once.
"Do not touch it carelessly," Mu Qingxue said.
"Excellent advice," Mo Qian replied. "The kind I prefer hearing before anyone touches it carelessly."
Gu Tian stepped around the perimeter, reading the broken sigils carved into the floor. "Transmission node," he muttered. "A linked pillar. Not the core itself. Something that answered to something else."
Lin Yuan studied the pillar in silence. He could feel, rather than understand, that they had reached one of the mountain's true buried joints. Not the heart. Not the source. A node. A place where commands had once passed, where force had once moved.
The medallion warmed.
He drew the incomplete fragment from its casket and raised it slowly.
The pillar answered immediately.
Light surged up the inner veins, not violently but with the steady strength of a body recognizing blood. Dust shook loose from the ceiling. Hairline cracks in the floor filled with dim silver radiance. The air thickened.
Then a second mechanism awakened.
A panel in the far wall split apart with a grinding sound that sent everyone's hands toward weapons. Beyond it lay a smaller chamber lined with shattered crystal slates and the remnants of what had once been a mural large enough to cover the entire wall. At the center, on a broken pedestal, rested a single intact crystal the size of a clenched fist.
Mu Qingxue's voice dropped. "A memory crystal."
Gu Tian's eyes hardened. "If it still holds anything after all this time, we learn more from that than from ten dead maps."
They entered the chamber together. The mural fragments were damaged beyond full reconstruction, but enough remained to make their blood run colder. A mountain much like theirs stood at one edge of the painting, connected by lines of light to distant peaks, towers, gates, and sky-bound platforms. Figures in ceremonial robes raised seals beneath a star-pattern canopy. In the center, stylized above them all, was a formation-heart motif—layered circles around a core of concentrated power.
Lin Yuan did not need anyone to tell him this place had once belonged to something greater than a forgotten frontier ruin.
Bai Lian lifted the crystal with both hands, careful and reverent. It pulsed weakly, then projected a fractured image above the pedestal: columns, sealed routes, a central chamber deeper below, and script too damaged to read in full. Mu Qingxue caught what she could. Gu Tian caught more. Lin Yuan caught the shape of one line that repeated in every fragment:
heart node.
The image broke, returned, then showed another sequence—part of the network being cut. Not by collapse. By violence. Lines extinguishing one after another. Seals falling. Routes dying. A retreat. A deliberate severance.
When the crystal dimmed, no one spoke for several breaths.
At last Gu Tian said, "Someone butchered this structure from the inside out."
Mu Qingxue nodded slowly. "And if this pillar still reacts, then at least one lower branch remained dormant instead of dead."
Mo Qian looked back toward the tunnel they had descended. "Our sect," he said, "is sitting on one branch of a buried giant."
Lin Yuan studied the mural's broken central pattern. "Not only sitting on it," he said quietly. "We are tied to it now."
He did not say the rest aloud: that the medallion had responded as if it knew the place. That the system had acknowledged each stage of discovery. That every step downward made the hidden line between his past and this mountain feel less accidental.
Su Wan was the one who finally broke the hush. "The pulse is stronger," she said.
Everyone felt it an instant later.
A slow throb passed through the floor, through the pillar room beyond, through the cracked walls and the air itself.
Not an attack.
Not a collapse.
Recognition.
The ancient route beneath the Primordial Firmament Sect had not truly awakened.
But it had moved.
Like an enormous buried body stirring one finger after centuries of stillness.