The wind in the passageway stopped.

Chen Hao took a step forward, his foot stepping on something and making a slight scraping sound. He looked down and shone his flashlight on it; it was a thin layer of dust on the ground. This place didn't seem untouched; it looked like it had been deliberately cleaned, yet these details were deliberately left unattended.

Susan followed behind, whispering, "Don't walk too fast, in case there are still traps."

“I know.” Chen Hao turned around, “but standing here in the cold wind isn’t a solution; we have to move forward.”

Carl walked at the back, the camera lens pointed straight ahead. Just as he was about to speak, the stone slab beneath his feet suddenly sank.

"Wait!" Chen Hao called out.

It's too late.

With a crack, the ground split open, collapsing more than three meters in the middle to form a deep crater. Chen Hao and Susan stood on the front, while Nana and Karl were separated on the other side. The two walls began to close inward, slowly but resolutely.

"Nana!" Chen Hao rushed over, lay down on the ground and reached out his hand, "Come here quickly!"

Nana lifted her leg to jump, but her right mechanical foot got stuck in a crack in the wall. She tried to pull it out, but it wouldn't budge. The wall continued to narrow, and the metal casing made a screeching sound.

"Don't pull it!" Susan shouted, "It'll break!"

Chen Hao quickly looked around and noticed that the camera bracket on Karl's shoulder was metal. "Take that off!" he pointed to the bracket. "Quick! Use it as a crowbar!"

Carl hesitated for a moment, then immediately took action. The moment the support was removed, Chen Hao took it and inserted it into the bottom of the wall crack, pushing upwards with force. Nana immediately understood his meaning, using the lever to lift her right leg while simultaneously pulling out the mechanical foot with a counter-force.

In the last second before the wall closed, she pulled her body backward, falling onto the ground behind her. The support frame was compressed into a V-shape and snapped with a crack.

“That scared me to death,” Carl gasped. “We almost really split up.”

“It’s not much better now.” Chen Hao stood up. “We’ve been cut in two.”

Susan crouched down at the edge of the pit and looked inside. "There's the sound of water at the bottom, it's probably a drainage channel," she said. "But the pit is too wide, I can't jump over it."

Chen Hao didn't answer, staring at the ground opposite him. The stone slab that triggered the trap was slightly raised, unlike the others. He picked up a piece of gravel and threw it at it, but there was no reaction.

“It’s not a continuous trigger,” he said. “You can only step on one at a time.”

“The problem is how to get across,” Susan said. “There’s no bridge, and we didn’t bring any rope.”

At that moment, the rock wall above them lit up.

Three lines of text appeared:

Three errors, permanent account closure.

**Current error: 1/3.**

Collaboration failed.

"It's keeping score?" Carl smiled wryly. "We just committed a foul, didn't we?"

"Even if it's not answering the question, it's still a foul," Chen Hao muttered. "This place is stricter than the exam."

Susan glanced at her watch. "The oxygen level has dropped to 87%," she said. "The rate of decline is not right."

“The air circulation in this confined space has been cut off.” Nana stood up. “The system is drawing away some of the gas, probably to force us to move.”

"So, if we don't move, we'll suffocate here?" Karl's voice trembled slightly.

“Theoretically, it shouldn’t cause suffocation,” Nana said, “but it could trigger a second lockdown, completely cutting off the road.”

"That sounds pretty dangerous too." Chen Hao stroked his chin. "Did the scene in that box before have a similar structure?"

“Yes,” Nana nodded. “The database records a type of ‘trial channel’ used to test team coordination. It usually has multiple isolation zones, and operations must be synchronized to reset.”

"So that means we have to move on both sides?"

"The possibility is very high."

Chen Hao immediately turned to Susan. "Look over there, see if there's any dent, like a handprint."

Susan brushed away the moss on the wall and, sure enough, found a palm-shaped groove. She turned and shouted, "Found it! One on the left!"

“I saw it too.” Chen Hao found the corresponding slot on the right. “It should be that they need to be pressed at the same time.”

“The problem is that it’s too far,” Susan said. “We can’t reach the other side from here.”

“You don’t need to reach it,” Chen Hao said. “Wait for me to say one, two, three, and then we’ll press it together.”

"It's that simple?"

"It's not simple, but there's no other way." Chen Hao took a deep breath. "I'll tell you when you're ready."

"alright."

"Nana, keep an eye on the changes in the ground over there."

"Ready in position."

"One, two, three—press!"

They both put their hands in at the same time.

The ground trembled, then a stone slab rose from the bottom of the pit, slowly extending forward. Another slab rose from the opposite side, gradually approaching. The two slabs met in the middle, forming a simple bridge.

"It's done!" Carl shouted.

"Don't get too excited yet." Chen Hao stared at the bridge. "This kind of place won't let you cross easily."

He crouched down and shone his flashlight on the seams of the bridge. The surface looked smooth, but there were some small holes along the edges, arranged in a regular pattern.

"It's like an air vent," he said.

“It’s not ventilation.” Nana approached and analyzed, “Those holes have resonant cavities inside, which may be sound wave devices.”

"What's the meaning?"

“Crossing the bridge will trigger a sound attack at a specific frequency.”

"Will it hurt someone?"

"Insufficient data, but the nervous system may be affected."

As they were talking, Karl stepped onto the bridge.

Buzz—

A deep sound wave rang out, causing a throbbing sensation in everyone's ears, and their steps involuntarily slowed. Chen Hao shook his head, feeling as if something was pressing down on it.

"Go back!" he shouted.

Carl staggered back to his original spot, his face pale. "My head is spinning...it feels like someone is banging a gong in my head."

“I can’t go on alone anymore,” Susan said. “I have to find a way to withstand this sound.”

Chen Hao suddenly remembered something. "Don't we have a coating on our bodies? The outer layer of our wetsuits."

"You mean that glowing membrane?" Susan asked.

“Yes. Nana mentioned before that it has a certain shielding effect on electromagnetic waves,” Chen Hao said. “Sound is also a wave, so it might be able to disperse the influence.”

“The human body is not a conductor,” Nana said. “But if we hold hands to form a circuit, we might be able to distribute the energy load evenly.”

“Then let’s hold hands and cross over.” Chen Hao extended his hand. “Whoever disagrees can stay.”

No one spoke.

The four lined up in a row, with Nana at the front. She felt no pain and had strong resistance to distractions, making her ideal leader. Chen Hao held her hand, Susan held Chen Hao's hand, and Carl was last, gripping Susan's wrist tightly.

"Let's go," Chen Hao said.

They stepped onto the bridge together.

The buzzing sound started again, this time seemingly more diffused. Chen Hao felt his head was still heavy, but he could still control his body. He stared at Nana's back and moved forward step by step.

Halfway across, the blue light on the bridge intensified, and the sound wave frequency changed. Susan paused, her hands tightening sharply. Chen Hao knew she was struggling, so he squeezed her hand back firmly.

"Don't let go," he said. "We'll be there soon."

The last stretch of road was walked extremely slowly. Everyone's breathing became heavy, and their steps dragged. But they didn't stop.

Finally, all four of them reached the other side.

The moment my feet touched the ground, a deafening roar came from behind. The entire stone bridge had snapped and plunged into a deep pit, splashing water everywhere. There was no way back.

"Looks like we're not allowed to turn back." Karl leaned against the wall, panting.

"We weren't planning on turning back anyway." Chen Hao wiped his sweat. "Check all the equipment to see if there's any damage."

Susan rummaged through her backpack to make sure all the tools were there. Carl remounted the camera tripod and tested the lens. Nana stood in front, scanning a door not far away.

“The space ahead has widened,” she said. “It should be the entrance to the main hall.”

Is the door open?

"Closed state. The surface has an array of symbols, consistent with the style of the previous map fragments."

"Another combination lock?"

"Uncertain. Further analysis is needed."

Chen Hao walked to the door and looked up. Above the door frame was an inscription:

"Those who travel together, enter; those who travel alone, stop."

"That's a really harsh thing to say," he said. "So, that last test was to see if we could walk together?"

“Obviously,” Nana said, “the door won’t open if only one person survives.”

"So all four of us have to be here?"

"That's highly likely."

Chen Hao turned to look at his teammates. "Then everyone stand in your positions and don't move around."

He reached out and placed his hand on the groove in the center of the door. Susan, Carl, and Nana followed suit, placing their hands on it one after another. The four of them stood in a row, their palms marked with different symbols.

A few seconds later, a red light appeared around the door crack.

Then, with a click, the heavy stone door slowly rose.

A colder wind blew out from inside.

Behind the door was an open space with neatly paved stone bricks on the ground, and at the far end was a high platform. Something was placed on the platform, covered by a transparent cover, so its contents could not be seen.

"There's still 82% oxygen left," Susan glanced at her watch. "Enough for a while."

"Don't rush in yet." Chen Hao stared at the platform. "Who knows if there are other mechanisms inside?"

“I can probe first,” Nana said.

"Wait a minute," Chen Hao stopped her. "Let me think about it."

He stood at the doorway, looking at the layout inside. The platform was more than twenty meters from the door, with nothing in between. It was too clean, unusually clean for a normal passageway.

“There’s definitely something wrong with the ground,” he said. “Either it will collapse when you step on it, or it will start to smoke as you walk on it.”

"How about we try throwing something?" Carl asked.

"What are you throwing?"

"I have a spare battery."

“Don’t waste it,” Susan said. “We might need it later.”

Chen Hao thought for a moment, then bent down, grabbed a handful of ash, and scattered it forward.

The dust fell to the ground, but there was no reaction.

He sprinkled it again, a little further away.

This time, the moment one of the dust particles fell, a very faint line flashed across the ground, disappearing in an instant.

"Did you see that?" he whispered.

"where?"

“The middle brick,” Chen Hao pointed, “has a seam along its edge, unlike the others.”

Nana pulled up the thermal image. "The temperature in that area is slightly lower," she said. "It might be the active panel."

“That’s a trap,” Chen Hao said. “Stepping on it with one foot won’t trigger it, but it will be triggered when both feet touch the ground.”

How do we get there?

“Crawl over there,” he said. “One at a time, hands and feet on the ground, spreading your weight out.”

"Are you serious?"

"Or you can fly there?"

Susan sighed. "I'll go first," she said, "because I'm the lightest."

She crouched down and slowly moved forward. One hand supported her on the ground, the other outstretched, her movements cautious. When she reached the brick, she deliberately placed one knee on the side, leaving the other leg dangling in the air.

There was no movement.

She continued forward and passed safely.

Carl went second, crawling across like her. Although his movements were clumsy, he successfully reached the other side.

When it was Nana's turn, she landed on all fours, her mechanical joints subtly adjusting their angles, and glided silently across the danger zone like a cat.

Finally, it's Chen Hao.

He had just bent down when his stomach got stuck. "Did these clothes shrink?"

"Stop talking nonsense," Susan urged from the other end. "Hurry up."

Chen Hao gritted his teeth and shuffled forward. As he approached the crucial position, he deliberately shifted his weight onto his left arm and right leg, lightly touching the ground with his left leg.

Just as he was about to pass through, his right elbow accidentally pressed against the edge of the brick.

The ground trembled slightly.

"Oh no."