Just then, a rapid succession of gunshots echoed in his ears, suggesting his companions on the shore had spotted the dangerous creatures behind them and opened fire.

Young Master Liu and Fan Debiao scrambled up onto the surface of the water, and Yang Weidong, already ashore, swiftly hauled both men up.

Looking back, the two men gasped in shock. A sleek, black, spindle-shaped aquatic creature was sinking to the bottom, emitting shrill squeals as the bullets struck it. Because it submerged so quickly, Young Master Liu couldn't get a clear look at the thing. The group watched as the entity disappeared beneath the water, never to be seen again, before they began to survey their current surroundings.

The spot where they emerged was a vast, circular pool resembling the mouth of a well. The area where they stood felt like a courtyard, enclosed by walls several meters high; judging by the beams of the flashlights, the space outside these walls was likely open air.

What startled them further was a black door set into the wall directly ahead—presumably the exit from this courtyard. Flanking either side were two massive, thick-trunked trees. Turning back, they saw a small white building standing starkly in the depths of the courtyard. Fan Debiao let out a low cry: "Mother of God, where is this place? It looks exactly like someone’s private courtyard. How can a place like this exist a thousand meters underground?"

Jia Zhuangyuan let out a cold scoff. "The ancients held the philosophy of treating death as life, especially the wealthy or those in power. They would build their tombs to resemble the places they lived, and some emperors even replicated their entire palaces underground, like Qin Shi Huang. Seeing a small courtyard like this is hardly surprising."

Fan Debiao nodded. "That's true, but how are these trees on either side growing without photosynthesis?"

Jia Zhuangyuan said, with a somewhat sinister tone, "You can go and see for yourself."

Fan Debiao grabbed Yang Weidong. "Dongzi, let's go take a look. This place gives me the creeps, you accompany me."

Yang Weidong, a guileless and straightforward man, casually accompanied Fan Debiao as they slowly approached. As they neared the trees, both men let out a sharp cry, spun around, and bolted back. They muttered breathlessly, "Mother of God, so many heads!"

Seeing their ashen faces and sheer terror, Jia Zhuangyuan chuckled dryly. "Did you get a good look at what those trees are?"

Fan Debiao and Yang Weidong shook their heads, unable to speak clearly. "No idea, didn't see clearly. We just saw lots of round human heads hanging on the trees—it scared us half to death."

Jia Zhuangyuan explained, "In the theories of Feng Shui and burial rites, this location would be termed an Yin Zhai (Shadow Dwelling), and these two symmetrically placed trees are called Yin Mu (Shadow Trees). These Yin Mu are not trees from the mortal world. They are sculpted shapes made from extremely hard materials, perhaps iron or bronze, used to substitute for the trees in a courtyard in the living world. Of course, for exceptionally wealthy figures, they might even use incredibly rare Yin Chen Mu (petrified, water-logged wood)."

Fan Debiao asked, "What is this Yin Chen Mu? And what does it mean that these Shadow Trees have human heads hanging on them?"

Jia Zhuangyuan replied, "This Yin Chen Mu is said to be a species of tree long extinct. Some claim it grows in the netherworld; others say it grows deep in the valleys of Kunlun where sunlight never reaches. Legend holds that Yin Chen Mu grows only a few centimeters every ten thousand years. Its wood is hard, dense, and exceedingly precious; it's said that an equal weight of Yin Chen Mu can trade for an equal weight of gold. Those round objects hanging on the Yin Mu are not actual human heads, as you might imagine, but merely spherical ornaments carved in the shape of a human head from some other material."

Seeing that Fan Debiao was about to press him further with more questions, Jia Zhuangyuan waved a hand. "Enough. We don't have time now to delve into Feng Shui and burial lore. This Yin Zhai is certainly the deceased's resting chamber in the afterlife, and we best not enter it. Let's open the courtyard gate and search for a way out."

The others agreed and walked toward the black courtyard door.

Suddenly, Jia Zhuangyuan interjected, "Wait everyone, something feels wrong."

The others turned back, looking at him in confusion. He stood there, brow furrowed, seemingly deep in thought. After a moment, he looked up, his gaze distant, and murmured, "An Yin Zhai, appearing within the passage leading to the entrance of the Boundless Demonic Treasury (Wuji Mozang)... this doesn't quite fit the style of a tomb. Where exactly is the inconsistency? Could my judgment be flawed?" It was evident that his confidence in the professional knowledge he had cultivated for over twenty years was shaken, leaving him with a trace of bewilderment.

Young Master Liu stepped forward, standing before Jia Zhuangyuan. "Senior Jia, the Boundless Daoist Repository (Wuji Daozang) is just a legend. We cannot explain it using our current experience and knowledge. Don't disparage yourself; finding the entrance from the volcanic lake already proves your judgment and experience played a crucial role. What we face now might be a realm no one has ever entered. We must all work together to unveil this age-old mystery."

Jia Zhuangyuan looked up at Young Master Liu, then took a deep breath and smiled. "Young Liu, you are right. Whether this is the Wuji Mozang or not, it is certainly one of the Three Great Secret Vaults. Perhaps the Boundless Daoist Repository is right before our eyes." With that, he signaled for the group to open the courtyard door. Cai Qingchong, at the front, placed his hand on the black door, then turned back. "To be safe, everyone stand to the sides; I’ll open it."

The others nodded and separated to stand on either side of the door. Cai Qingchong, leaning sideways, pulled the ring on the door. A deep, spine-chilling creak sounded as the door slowly opened, revealing absolute silence beyond.

Just as the group prepared to step out of the courtyard, a sudden, cold wind swept up from the ground. With another agonizing creak, the black courtyard door slammed shut with a bang. The group instantly felt a bizarre aura slowly seeping out from within the Yin Zhai.

Jia Zhuangyuan cried out, "Bad news!" Before the words had fully left his mouth, the vermilion door and windows of the white building slowly swung open in the eerie wind. And those two Shadow Trees, just like living trees in the mortal world, began to rustle their leaves with a distinct sound.

The group huddled tightly together, leaning against the sides of the courtyard door, raising their weapons and watching the Yin Zhai intently for any imminent change.

The whooshing cold wind grew stronger, and from inside the white building, a crisp sound, like the weeping of a child, suddenly emerged. In this grim environment, an icy chill sank to everyone's bones.

Suddenly, the weeping seemed to draw nearer. The group saw two children, both with their hair tied in high pigtails, holding hands, emerge from the red door of the small building. The pair—a boy in green and a girl in red—had unnaturally pale faces. They hopped and staggered toward the group, their cries piercing the silence.

Jia Zhuangyuan gritted his teeth and cursed under his breath, "Which heartless fiend placed two little ghosts to guard this Yin Zhai."

At that moment, the spherical objects resembling human heads hanging on the trees began to drop one by one with loud crackling sounds, rolling across the courtyard floor.

The two little ghosts abruptly stopped wailing, bent down, and each picked up a pitch-black sphere, shoving it into their mouths.

The others watched in utter astonishment as the two little ghosts revealed sharp, stark white teeth and crunched down on the head-like spheres, dark red fluid oozing down the sides of their mouths.

Jia Zhuangyuan suddenly snapped out of his shock and yelled, "Fire! Don't let them finish eating, or we’ll all be in danger!"

Hearing this, a wave of panic washed over the group. They hastily raised their weapons and began spraying bullets at the two little ghosts.

The two children, likely ancient spirits unaccustomed to modern weaponry striking them from such a distance, were instantly knocked to the ground by the barrage of bullets, dark red fluid slowly seeping from their bodies.

Just as the group let out a sigh of relief, thinking the ghosts defeated, the two children sprang up instantly. They shoved the unfinished spheres in their mouths and swallowed them whole. Though bullet holes still oozed dark red fluid, they began to weep loudly again and continued staggering toward the group.

The others panicked. These two little ghosts were unkillable—what was happening? The guns in their hands roared again, but strangely, the bullets failed to knock the pair down this time; they merely staggered momentarily before pressing onward. At this point, everyone was truly dumbfounded. Jia Zhuangyuan shook his head. "I didn't expect these two little ghosts to be satisfied by just one Yin Guo (Shadow Fruit). Old Jia is truly cursed. Alas, I must handle this myself."

Saying this, he reached into his backpack, producing a dark, round object in his left hand and a thin, rope-like implement resembling a whip in his right. He walked toward the two little ghosts.

The two children continued to cry out at the top of their lungs, their mouths agape, their stark white teeth stained with splotches of dark red blood. They extended four small hands toward Jia Zhuangyuan, as if asking to be picked up. Suddenly, the group watched as the children's hands slowly curled into claws, and their fingernails grew at an alarming rate, reaching seven or eight centimeters in the blink of an eye.

The others watched this bizarre scene tensely, unsure what would happen next, genuinely worried for Jia Zhuangyuan.

Jia Zhuangyuan stopped about a meter and a half away from the two little ghosts and let out a cold snort. "Little ghosts, do you wish to mutate? Old Master Fei specializes in collecting ghosts."

With that, the whip-like implement in his hand whipped out in a circle, accurately looping around the neck of the red-clad girl. He quickly yanked her toward him, while simultaneously shoving the dark round object held in his other hand swiftly into the little girl's gaping mouth.

The girl’s wail was immediately muffled by the object in her mouth, turning into a mournful whimper. Jia Zhuangyuan rapidly pulled the girl backward, retreating while shouting, "Shoot the little boy! Don't let him get close enough to take her hand again!"

Yang Weidong and Fan Debiao immediately raised their guns and fired wildly at the green-clad boy. The girl, held fast by Jia Zhuangyuan’s whip, choked on the object in her mouth, whimpering, and her footsteps began to falter. Her body seemed to be undergoing a drastic transformation; her previously pale complexion began turning black and purple around her face and neck, spreading downward.

She began to struggle violently, her small hands gripping the whip around her neck, shaking her head desperately to break free. This little ghost possessed astonishing strength, forcing Jia Zhuangyuan to exert all his energy, sweat pouring down his face, just to hold her back in the tug-of-war.

Meanwhile, the green-clad little ghost snarled, waving its two small hands—no, they were definitely ghost claws now—and darting toward Jia Zhuangyuan with a hissing sound. It moved with incredible speed; even the dense spray of bullets only slightly impeded its mobility.

Seeing it about to reach the red-clad ghost, Jia Zhuangyuan urgently called out, "Find a way to trap him! If the two ghosts hold hands again, all my effort will be wasted."

At that moment, a blur flashed past the group. Cai Qingchong lunged toward the green-clad ghost, dagger in hand. The blade emitted a strange glow as he hurled it toward the ghost’s head.

The little ghost swiftly sidestepped, dodging the attack. It then bared its teeth at Cai Qingchong and shot both hands forward, grabbing his dagger with astonishing speed. It let out a shrill cry, pulled the dagger toward its chest, and extended its head along the line of the blade to bite at Cai Qingchong’s hand.

Cai Qingchong was startled and tried to yank the dagger up and away, attempting to break free from the ghost’s grasp and avoid the snapping jaws. But the dagger wouldn't budge an inch. The ghost's razor-sharp teeth were already near his hand. Heart pounding, Cai Qingchong instinctively let go of the dagger.

The green-clad ghost tossed Cai Qingchong's weapon to the ground with apparent glee, looked up, let out a piercing cry, its blood-red eyes fixed menacingly on Jia Zhuangyuan, and then lunged toward him with both arms spread wide.

Suddenly, Young Master Liu let out a sharp whistle and leaped into the air, landing between the green-clad ghost and Jia Zhuangyuan, shouting, "Evil spirit, how dare you be so presumptuous!" He raised a newly drawn talisman toward the ghost, and his Gang Qi (a protective energy field) erupted instantly. The talisman snapped straight, hissing as it sliced through the air.

The little ghost seemed to recognize the Daoist Gang Qi—after all, Daoists specialized in capturing demons and driving out ghosts. It executed a flawless backflip, narrowly evading Liu’s lightning strike.

Upon landing, it suddenly began to wail loudly again. This cry wasn't as piercing or frantic as before, but it carried a deeply unsettling sensation. As the crying resumed, the small courtyard was suddenly beset by a raging cold wind, and all the spherical head-like objects on the ground instantly lifted into the air, revealing grotesque faces, flying toward the group like a sudden, violent storm.

Liu let out a cold snort, waved both hands, and recited a long incantation. Instantly, all the human heads seemed to lose their power, crashing down around the group with repeated crackling sounds.

Liu turned back to face the green-clad ghost. For some reason, the ghost began to whimper softly and slowly retreat backward, appearing extremely fearful of the current Liu Da Shao.

Liu watched until the green-clad ghost had retreated back into the doorway of the white building before slowly walking to where the red-clad ghost and Jia Zhuangyuan were locked in a desperate tug-of-war. He said to Jia Zhuangyuan, "Senior, let her go. These two little ghosts are pitiful souls."

Jia Zhuangyuan paused, then released the whip-rope. The red-clad ghost glanced at Liu with its blood-red eyes, violently tore the rope from its neck, and—still clutching the dark sphere in its mouth—bolted toward the white building.

Just then, the doors and windows of the white building silently closed. The chilling wind inside the Yin Zhai ceased. Apart from the scattered round objects resembling heads on the floor, everything appeared as if nothing had ever happened.

Jia Zhuangyuan shook his head silently, bent down to retrieve the whip-rope and Cai Qingchong’s dagger. He handed the dagger back to Cai Qingchong and told the group, "The two little ghosts will no longer obstruct us. We can leave the Yin Zhai and continue on our way."

Cai Qingchong walked to the door and gently pulled open the black courtyard gate once more.

As the gate opened, the first thing that greeted them was a long street, paved with strips of blue-gray flagstones, flanked on both sides by ancient residential houses of varying heights.

The group filed out of the Yin Zhai. The black courtyard door closed silently the moment the last person stepped out. Standing on the long flagstone street, they realized they seemed to have entered a closed-off dead end: uniform brick walls, uniform blue paint, with only a single, extremely thick stone door tucked away in a corner.

"Does anyone here know mechanisms? This stone door is complicated! If we can't open it, we'll be trapped here forever," Jia Zhuangyuan mused after a moment of silence.

Everyone remained quiet, as they were utterly ignorant about ancient underground structures when confronted with Jia Zhuangyuan’s question.

Jia Zhuangyuan looked at the silent group helplessly, then shook his head. "It seems I must solve this puzzle myself. You can offer me no assistance." He then walked up to the bare stone door and began inspecting it closely.

The others stood behind him, exchanging glances, feeling quite helpless. They genuinely lacked any experience with underground ancient architecture and had no valuable suggestions to offer Jia Zhuangyuan.

Jia Zhuangyuan circled the stone door for a while, then turned to them. "The person who installed this stone door was definitely a master. Opening it likely requires finding a mechanism, and one that is extremely intricate and perilous."

Saying this, he asked the group to shine their flashlights where his hands were, and he began slowly tracing his fingers over the stone walls flanking the door.

A moment later, he exclaimed in surprise, "Found it!"

Everyone crowded closer, eager to see how the ancients devised the mechanism capable of opening this several-thousand-pound stone door, and how it was constructed.

Jia Zhuangyuan shouted, "Focus all your flashlights on the spot where my hand is!"