The stone slab beneath his feet had just cracked open, and before Chen Hao could even utter a curse, Nana's lamp swept over him.

"Don't move." Her voice didn't change, but she had already taken a half step to the side, blocking him from the crack. "The load-bearing surface is spreading."

He looked down and saw the thin crack spreading outwards like a spider web, with grayish-white powder dripping down from the edges. If he hadn't pulled his foot back quickly, he'd probably be stuck in the hole screaming for help by now.

"Is this place made of paper?" He slowly moved back. "It'll fall apart if you step on it twice."

Nana didn't reply. Suddenly, the ring light on her shoulder switched to a wide-angle mode, and a circle of blue light swept across the ground, as if painting the entire cave wall with a thin layer of paint. Her back arched slightly, and several thin metal rods extended out, forming a small radar array that emitted a low-frequency hum.

"The 3D mapping has begun," she said. "We expect to complete the main channel modeling in eight minutes."

"Isn't this just a mobile property appraisal?" Chen Hao patted his pants. "How about we rename it 'Sister Na's Property Appraisal'? The kind that specializes in appraising dilapidated houses."

She ignored the joke, tapped her finger lightly in the air, and a semi-transparent data graph was projected directly onto the rock wall: a winding passage branched into three paths, a red dot marked the location of the main hall, and the area beneath their feet was painted yellow with the words "structurally unstable" written on it.

“Mark the path.” She handed over a piece of charcoal.

Chen Hao took it and drew a crooked "1" at the nearest fork in the road. Then he took a few more steps forward and wrote a "2" at the second fork, thoughtfully adding an arrow.

"My handwriting is worse than a primary school student's fill-in-the-blank test," he muttered. "If you actually stored it in a database, future generations would think it's a relic of a primitive civilization."

“It’s been entered,” she said. “The annotations are clear and meet the recording standards.”

He rolled his eyes, casually tied one end of the rope to a protruding rock, and the other end to his wrist. It was an old climbing rope he'd salvaged from the base; although badly worn, it could still hold its own for a while if straightened.

“We’re in a similar situation to lab rats right now.” He tugged at the rope. “You’re scouting ahead, and I’m running behind you, having to memorize the route. The only thing missing is a number around my neck.”

"Your number is b-07." After she finished speaking, she walked away without looking back.

Chen Hao was taken aback for a moment, then burst out laughing: "You actually have a record?"

"Temporary allocation." She paused for half a second, "to facilitate the tracking of operational efficiency."

The main passageway widens as you walk further in, and the ceiling is so high you can't see the top; you can only see a blurry outline illuminated by the lights. The ground gradually becomes flat, but it's very slippery, so you have to test your footing with every step.

After making a sharp turn, the view suddenly cleared up.

A large hall stretched out before him, its surrounding rock walls gleaming with the light of water stains. In the very center, a dark gash tore through the ground, its depths unfathomable. Chen Hao had just peered forward when the beam of his headlamp shone down, disappearing after a distance of thirty meters.

"Good heavens." He took a step back abruptly. "Is this a courier channel to the underworld? You don't even need to pack a package to send someone."

Nana had already crouched down, and a small disc with a string popped out from her wrist. She gently placed it down, and the disc slowly descended, the markings on the string gradually disappearing.

"The probe has descended forty meters and touched the bottom." She looked at the data stream. "The bottom is a layer of rubble, with no signs of life and no air movement."

"In other words," Chen Hao swallowed, "you won't get eaten if you fall, but you'll be smashed into a meat pie."

“The conclusion is correct.” She stood up and projected a circle of red dotted lines on the ground. “Safe distance is more than three meters. Do not approach.”

“You’re quite good at highlighting key points.” He walked around the cordon, shuffling along the wall. “But why is this hole located here of all places? Right in the middle of the road, it looks like a trap someone deliberately dug.”

"It's the result of a combination of geological fracturing and dissolution," she said. "It's not a human-made design."

“But it just happened to be like that.” He glanced back at the black hole. “It’s like the last big question on an exam. You know you can’t touch it, but you still have to get close to see if you can do it.”

They continued along the rock face, where three narrow side passages appeared ahead, like three half-closed mouths. The one on the left was blocked by collapsed rubble, the middle one was too low and they had to climb in; the one on the right was slightly wider, but the entrance sloped upwards, with a steep incline like a stairwell on fire.

Nana pulled up the infrared image and pointed to the side tunnel in the southeast direction: "There is a weak airflow here, and the temperature is one degree lower. It is speculated that it is connected to other cavities."

"Where there's wind, there's a way." Chen Hao rubbed his hands together. "Maybe there's an underground agritainment business hidden behind it."

He put on gloves, walked to the pile of rubble, bent down and moved a stone the size of a bowl. Then he pushed away a flat piece of rock, his movements not exactly nimble, but steady.

Nana stood by, ready to take over at any moment. A sharp stone rolled down, grazing his arm, and his coat ripped open with a "rip".

"Ouch!" He pulled his hand back. "This stone is quite vengeful."

“The skin is undamaged.” She glanced at it. “I recommend changing your protective gear.”

"Change what? I only have two clothes, one patched upon patched, and the other just torn." He snorted. "Besides, we're doing exploration now, not shooting a fashion shoot. So what if it's torn? Scars make us look professional."

He continued moving the stones, sweat streaming down his forehead and dripping onto them, where it was instantly absorbed. The two of them worked together to clear a gap just wide enough for one person to pass through.

Nana went in first, walked ten meters, and then stopped to scan.

“The structure is stable and there is no immediate risk.” She turned around and said, “It is passable.”

Chen Hao followed, crouching low as he moved forward. The passage wasn't long; after about twenty meters, it connected to a small cavity. The ground was slightly higher than the main path, like a naturally raised platform.

"There's a chair here." He plopped down. "I'll rest for a bit and think about how to make a living."

Nana didn't sit down. Instead, she unfolded the radar and recalibrated it, marking the newly discovered side tunnels on the map and labeling them "to be explored further."

“The main area mapping is complete,” she said. “A total of seven branch roads were recorded, four of which are dead ends, two are blocked by collapse, and one has the potential to be extended.”

“Seven out of one, the odds are even lower than winning the lottery.” He looked up. “But at least we’ve figured out the situation. The other places were so bad they’d collapse in the wind and rot in the rain. Unlike this place, it’s sturdy, but it’s a bit tough on your legs.”

He stood up, stretched his shoulders, the rope still tied to his wrists, swaying gently with his movements.

"Should we go back to get our equipment now, or continue exploring a bit further?" he asked.

“I recommend turning back,” she said. “We currently have 37 percent of the current lighting remaining and sufficient oxygen reserves, but our physical exertion has reached a critical point.”

"Critical threshold?" He grinned. "You mean I'm going to fail?"

"Your breathing rate has increased by 22 percent, and your muscle fatigue index has risen."

“That’s because I was moving stones!” he protested. “It’s not like I was exhausted from walking. Besides, with my build, I naturally consume more oxygen, it’s normal.”

As he spoke, he took two steps forward, and suddenly his foot slipped.

It wasn't that the stone was loose, nor that the ground had collapsed—it was that the sole of his shoe had hit something round.

Looking down, I saw a small pebble, grayish-white, with a smooth surface, as if it had been washed by water for a long time.

The problem is, there are no traces of water flow here.

He bent down, picked it up, and looked at it in his palm.

“Strange,” he said. “This kind of stone…shouldn’t be here.”

Nana's light immediately swept over.

Before he could speak, another pebble of the same kind rolled out from a crevice in the rocks at his feet.