The boat continued forward, and the light on the water grew denser, as if the entire sea had been illuminated.

Chen Hao leaned against the control panel, his eyes fixed on the screen. The blue light outside rippled outwards in layers, like someone turning on lights underwater. He stroked his chin and said, "I haven't seen a single mosquito in this place, but there are streetlights."

Nana ignored him, her finger sliding across the control panel. She switched the detection mode to passive reception and said in a low voice, "Magnetic field interference has increased, and the navigation error has widened to five degrees."

“Then don’t trust the navigation.” Susan looked up. “Follow the light. That big guy didn’t just clear this road for us to see the sea view.”

Carl stood beside the emergency hatch, pliers in hand, inspecting the hull of the miniature probe. He tightened the last screw and said, "The probe is usable now. The antimagnetic layer has been doubled, and the cameras have been replaced."

“Okay.” Chen Hao straightened up. “Don’t send the main force yet. We’re not qualified to enter their living room. Let the little guy scout ahead first.”

Nana nodded and entered the command. The indicator light on the control panel turned from red to green, and the miniature probe slowly slid into the water from its side cabin.

The connection is established, and the dark seabed appears on the screen. The camera slowly zooms in, revealing undulating sand dunes with occasional trickles of water. Suddenly, a slab of rock half-buried in the mud is revealed.

"Stop!" Susan shouted.

The image freezes. The stone slab has neat edges and a ring of regular lines carved into its surface, clearly not formed naturally.

“Artificial.” Carl leaned closer to the screen. “This thing has been buried for who knows how long, but the marks are still clear.”

“And the direction is consistent.” Susan pointed to the image. “Look at the direction of the surrounding sand flow. This slab was deliberately placed here; it wasn’t swept over.”

Chen Hao scratched his head: "Who would put up a sign in this godforsaken place? What would it say?"

“A rubbing is needed,” Nana said. “Direct scanning will be affected by the magnetic field, resulting in incomplete data. Manual sampling is necessary.”

“I’ll go.” Carl put down his pliers. “Put on protective clothing and bring the collection kit.”

"Are you alone?" Susan frowned.

“Two people are too crowded.” Karl was already walking towards the equipment room. “Besides, the ships can’t be too close together. I’ll be right back.”

Ten minutes later, Karl emerged from the airlock, carrying an oxygen tank on his back and a box in his hand. He walked step by step towards the location of the stone slab. In the shot, his shadow was elongated by the faint blue light below.

Upon reaching the stone slab, he squatted down, opened the box, and took out a thin piece of paper and a soft brush. He gently swept away the surface sediment, then stuck the paper on and pressed it flat little by little with the brush.

"It's done," he said into the communicator.

"Come back," Chen Hao said.

Carl turned around, took a step, and slipped. He looked down and saw a crack in the ground, from which the same blue light shone through.

"Wait," Nana suddenly called out, "Don't move."

Carl stopped.

“Under your feet,” Nana zoomed in on the image, “that’s not a crack, it’s a structural joint. There’s something underneath.”

Chen Hao also noticed: "This land... is it pieced together?"

Susan quickly flipped through her notebook: "The terrain of the entire area is arranged in a hexagonal pattern, which I didn't notice before. Now it looks like the basic framework of some kind of building complex."

"So," Chen Hao grinned, "we're on top of a roof?"

No one laughed.

Carl carefully retreated, returning to the ship with the rubbing sample. He removed his outer protective suit and handed the paper to Nana.

Nana placed the rubbing on the scanner and activated the offline database. A large number of symbol comparison tables began scrolling across the screen.

Time passed second by second.

“It’s a match,” she said. “This symbolic system doesn’t belong to modern civilization, nor is it a known variant of ancient writing. It comes from a prehistoric marine group that was active around the end of the last Ice Age. Their language was based on circular symbols and emphasized the relationship between space and the flow of energy.”

"Has it been translated yet?" Chen Hao asked.

“Decoding.” She tapped her fingers on the keyboard. “The meaning of the combination is— ‘The hiding place can only be reached by the silent.’”

"A treasure trove?" Chen Hao raised an eyebrow.

“The probability is very high.” Nana continued operating. “There is another sequence of coordinates that points to a deeper part of this area.”

“The Silent Ones?” Susan read it aloud. “Does it mean people who don’t send signals? Or… people who don’t speak?”

“Whatever it is,” Carl said, looking at the screen, “that big thing made way when we turned off the engine.”

“Yes.” Chen Hao laughed. “We’re the silent ones, the professionals.”

Nana pulled up the map and located the coordinates. The red dot landed near an underwater cliff, where there was a narrow crevice of unknown depth.

“Here’s the problem,” she said. “The boats can’t get in. The crevice is less than three meters wide, and the rocks on both sides are sharp; forcing their way through would damage the hull.”

"Then send another small boat," Chen Hao said.

“No,” Carl shook his head. “The circuitry already showed signs of overheating during that flight. If we go back in, and it gets stuck or loses power, the equipment will be ruined.”

"Then let them go down," Chen Hao said.

"Are you crazy?" Susan looked at him.

"I didn't finish my explanation." Chen Hao shrugged. "Send a device that can resist interference, is small in size, agile in movement, and preferably can transmit real-time images."

“You mean…” Susan looked at Nana.

Nana stood up: "I can go."

"You?" Chen Hao was stunned.

“My machine has electromagnetic shielding capabilities, and its core system is independently powered. As long as it doesn’t suffer extreme physical damage, it can continue to operate,” she said. “Moreover, I can directly connect to the main control console and transmit data in real time.”

“But aren’t you…” Susan hesitated for a moment, “not quite suited for this kind of work?”

"What do you mean?" Nana turned to look at her.

“Well…” Susan said a little awkwardly, “you look quite expensive.”

Chen Hao chuckled: "She's right. If you break down, the repair costs will be more expensive than my life."

“I’m not a expendable item,” Nana said expressionlessly. “But if the mission requires it, I’m willing to take the risk.”

“Wait,” Karl suddenly spoke up, “She doesn’t need to go.”

He walked to the tool cabinet, pulled open a drawer, and took out a palm-sized mechanical device. It looked like a flat box with two small thrusters underneath.

"What is this?" Chen Hao asked.

“I modified it myself.” Carl placed the device on the table. “It was originally an inspection robot used to check the inside of pipelines. It’s small, lightweight, and the shell is made of titanium alloy composite material, which can resist certain magnetic field interference. I also replaced the camera with a deep-sea-specific model.”

"When did you do this?" Susan asked in surprise.

“Yesterday,” Carl said, unscrewing the back cover and plugging in the power to test it, “I knew then that we were bound to have to find a way out sooner or later.”

Chen Hao laughed: "You really are forward-thinking."

“It’s just a habit.” Carl turned on the machine, and the image immediately transmitted to the main control screen. “Let’s test the signal.”

The screen lights up, displaying a simulated image of the passageway ahead.

"Okay," Chen Hao decided. "Let it in."

After five minutes of preparation, the robot was released from its side compartment and slowly descended towards the cliff crevice.

The camera zooms in slowly. The rock wall gets close to the frame, its surface covered in scratches, as if it had been rubbed against something for a long time. The further in you go, the brighter the blue light becomes.

“The energy reading is rising.” Nana stared at the data. “There are stable fluctuations inside, and the frequency resonates with the slate symbols.”

The robot continued forward. The crack twisted and turned several times before finally arriving at a relatively open space.

Directly in front of you is a flat rock wall with a recessed circular structure embedded in its surface, the size of which is exactly the same as the symbol on the stone slab.

“That’s a door,” Susan whispered.

“And it can be opened.” Chen Hao stared at the center. There was a faint blue light there, flickering slowly, like breathing.

The robot approaches, its camera aimed at the groove.

“The match rate is 98%,” Nana said. “This structure is used to identify symbols. As long as the correct mark is placed, the activation mechanism will be triggered.”

“That’s the key.” Chen Hao looked at the rubbing paper on the table.

“Not necessarily,” Nana said. “It may require specific conditions, such as silent approach, no active signal transmission, or other unknown limitations.”

“Anyway,” Carl said, looking at the screen, “we’ve found it.”

“Yes.” Susan closed the notebook. “The ruins have been confirmed to exist, the clues have been deciphered, and the entrance to the secret chamber has been found. Next, how do we get in?”

Chen Hao didn't speak, staring at that point of blue light for a long time.

Then he turned around, opened the locker, and took out a spare set of protective clothing.

"What are you doing?" Susan asked.

"Change your clothes," he said. "I'm going to see what's hidden behind that door."

“You can’t go alone,” Nana said.

“I know.” Chen Hao zipped up his jacket. “That’s why I asked you to come with me.”

Nana glanced at him and walked towards the equipment area.

Carl began inspecting the second batch of detection equipment, packing three spare batteries into a waterproof bag. Susan rechecked the logs, marking three potential risks: changes in energy field intensity, the possibility of passageway collapse, and the unknown activation mechanism of the access control system.

Inside the control room, the four people were busy with their own tasks.

On the screen, that little bit of blue light was still flickering.

Chen Hao put on his helmet and tested the communication channel.

“The signal is normal,” he said.

"The oxygen will last for two hours." Carl handed him a compressed gas canister.

"That's enough." Chen Hao slung his gear over his shoulder. "Let's go."

He walked towards the airlock, his steps steady.

Nana followed behind, and the machine entered low-power mode, turning off the external lights.

Susan pressed the record button: "At 5:43 PM Beijing time, the expedition team is preparing to enter the outer perimeter of the core area of ​​the ruins, with the target being the unknown structure at the entrance to the secret chamber. Currently in good condition, all personnel are on duty."

Carl stood in front of the control panel, his hand resting next to the emergency recall button.

Chen Hao and Nana entered the airlock, the door closed, and decompression began.

The sea outside was a deep blue.

The robot was still standing in front of the door, its camera pointed at the groove.

A blue light flashed.

Chen Hao raised his hand and put the rubbing paper into the sealed bag.

He said to the camera:

"We're about to open the door."