After the red light went out, the cave was quiet for a few seconds.

Chen Hao didn't speak, but slowly withdrew his hand from the rock wall, as if afraid that touching it again would cause the entire wall to explode. He looked down at his palm, then looked up at Nana.

"Is it... frozen?"

Nana stood beside the circular device, the scanner still running. Her robotic arm rotated slightly, aligning with the newly appeared symbol at the bottom.

“No energy output was detected, but the data transmission was completed,” she said. “We received the data.”

"Did that flickering light just now count as a successful boot?"

"It counts as half a time."

Chen Hao sighed and squatted down beside her. The circle of symbols was deeply engraved with neat edges, not like it was chiseled out with tools, but rather looked like it had been directly burned onto the metal surface by some high-temperature rays.

"Did you write it down?" he asked.

"Save everything." Nana brought up the projection interface. "Comparing the ancient civilization coding system in the database."

"Any results yet?"

“There’s a partial match.” She pointed to a string of characters on the screen. “This phrase, ‘Observer has arrived,’ belongs to the common communication protocol of the Late Pre-Era Science Alliance and is often used in the automatic identification system of remote monitoring stations.”

"So...they were waiting here all along?"

“It’s not waiting for someone,” she said. “It’s waiting for the ‘observer’.”

"Is there a difference?"

“Yes.” Nana looked at him. “They’re setting an identity, not a point in time.”

Chen Hao frowned. "You mean, as long as someone meets certain conditions, this system can recognize them?"

"That's theoretically true."

He stared at the circle of symbols for a few seconds, then suddenly chuckled. "So, I've accidentally become the standard answer?"

“You triggered the activation sequence,” she said. “The position, intensity, and sequence are all within the threshold range.”

"So I'm actually pretty accurate?"

"It's purely a coincidence."

"Thanks, even robots can be discouraging."

Nana didn't respond, but instead turned to the rock wall. She activated the probe sphere, letting it fly low close to the wall. A faint blue light shone from the sphere's surface as it began scanning the mural line by line.

Chen Hao stood up and stretched his limbs. The temperature inside the cave was stable, but he still felt a little stiff. He walked to the wall and shone his flashlight on the carvings.

"What are these paintings... supposed to be about?"

"The overall content cannot be determined at this time," she said, "but it is certain that this is not decoration."

"How did you figure that out?"

“The arrangement.” She pointed to the first set of patterns, “The spiral pattern repeats seven times, with an additional arc added to the outer edge each time, like a progress bar.”

"So it's counting?"

"It may be recording some kind of periodic event."

The probe ball flew to the third zone and suddenly stopped. Nana's screen flickered and a new image popped up.

“A hidden layer has been discovered,” she said.

"What do you mean?"

“What you see with the naked eye is just the surface oxidation marks.” She adjusted the parameters. “There is a more intricate layer underneath, which can only be seen with multispectral imaging.”

The image gradually became clearer. The originally blurry lines transformed into complex geometric structures, resembling some circuit diagrams and others architectural cross-sections.

Chen Hao leaned closer to examine it. "This thing... the more I look at it, the more it resembles the layout of our base?"

“It’s not just similar,” she said. “It’s the prototype.”

"Don't scare me."

“The central circular structure perfectly matches the current silicon alloy device.” She zoomed in on the image. “The six branch channels around it correspond to energy, ventilation, storage, living area, research room, and emergency exit.”

"So this place... is a blueprint?"

“These are the blueprints for an underground shelter,” she said. “It was built approximately 2,300 years ago.”

Chen Hao was stunned. "More than two thousand years ago? Back then, humans were still using kerosene lamps, right?"

“Some regions are indeed in the early stages of industrialization,” she said. “But some isolated civilizations may have achieved technological leaps.”

"Who would build their house like this for no reason?"

"Survival needs after environmental degradation."

"But it's all snow outside, there isn't a single tree. What do they eat to survive?"

"The answer may lie behind the mural."

The probe continued forward, flying to the fifth relief area. Here, the patterns had changed; they were no longer architectural structures, but rather scenes of human activity.

A group of people stood around a tall tower, holding glowing rods in their hands. A beam of light shot into the sky from the top of the tower.

"Is this... generating electricity?" Chen Hao asked.

“It’s closer to energy harvesting,” she said. “The tower’s structure resonates with the atmospheric ionosphere, which could be used to absorb cosmic radiation and convert it into electricity.”

"It sounds like a science fiction movie."

"But the principle is feasible."

In the next scene, the city begins to collapse. The ground cracks open, the sky darkens, and people drag boxes underground.

“Environmental collapse,” Nana said. “Resource depletion leads to the migration of civilizations.”

"And then they went underground?"

"Long-term residence".

The probe ball flew to the last area. The rock face here was severely damaged, with large sections having crumbled away. Nana switched modes, using a particle reflection enhancement algorithm to reconstruct the rock.

The images slowly pieced together. It was a star map.

Chen Hao leaned closer to look. "What's this? A constellation?"

“A map of star distribution,” she said. “After calibration, the error is less than 0.3 degrees.”

Can you recognize it?

“Yes.” She imported the data into the astronomical database. “It’s completely consistent with the current night sky of the planet.”

"So...they're also on this planet?"

"That's right."

In the center of the star chart is a marker point, drawn as a small circle, surrounded by three wavy lines.

Nana entered the coordinate conversion program. A few seconds later, a set of numbers appeared on the screen.

She stared at it for two seconds.

Chen Hao sensed something was wrong. "What's wrong?"

“This location,” she said, “points to our current base.”

"ha?"

“Precise matching,” she said. “The error range is within ten meters.”

Chen Hao took a step back. "You mean... they knew all along that we would build a base?"

“It’s not that I knew,” she said, “it was a preconceived notion.”

"What do you mean?"

"They left this mark so that people could find it."

"But our site selection was random! How could people from two thousand years ago possibly have guessed the result of a comprehensive calculation involving terrain analysis, resource distribution, and safety factors?"

“Maybe it’s not a guess,” she said. “Maybe it was all part of the plan.”

Chen Hao fell silent.

He looked at the star chart again. The small circle sat quietly in the center, like an eye, watching over the present from the past.

"So we weren't the first ones here?"

“You are the second human to breathe,” she said. “I am a robot.”

"You really want to compete with me for this ranking?"

"I'm just stating the facts."

"But who would do something like that? Go through all that trouble carving a bunch of walls, leaving a signal, only to have someone come and flip a switch years later?"

"It might be to convey a message."

"To whom should it be sent?"

"Pass it on to someone who can understand it."

"So, do you understand now?"

"You only understand the beginning," she said. "The real content is probably hidden deeper inside."

Chen Hao looked down at his hands. The spot where he had touched the wall was still a little numb, like residual static electricity.

"So...did I just do something I shouldn't have done?"

“You have completed the verification process,” she said. “The system has confirmed the existence of the ‘observer’.”

"Then what?"

"Wait for further instructions."

"Whose orders?"

"have no idea."

The cave fell silent. Only the probe ball continued its slow movement, its blue light sweeping across the rock walls as if reading a long-dormant piece of code.

Chen Hao sat down against the wall. He felt a bit of a headache, as if his head was stuffed with a bunch of indigestible information.

"Nana".

"Um."

"Do you think... we might just be guinea pigs in someone else's experiments?"

"There is currently no evidence to support this conclusion."

"But it all seems too coincidental. Blizzard, valley, vein, footprints, cave, murals, device, signal... and finally, it all points to our base."

“Coincidence is one possibility,” she said, “but it could also be design.”

"If it's design, then who is the designer?"

"No record found in the database."

"Have you ever considered... that maybe we weren't here to explore at all?"

"no?"

"Perhaps we were summoned here."

Nana turned to look at him.

"You mean, we are the summoned observers?"

"Otherwise what?" Chen Hao smiled wryly. "How do you think this fat, nerdy guy and broken-down robot duo survived in this godforsaken place? Luck? Hard work? Or did some ancestor write a line of code two thousand years ago saying, 'Let these two in when the time comes'?"

Nana didn't answer. She simply brought up the set of symbols again and compared them repeatedly.

A few seconds later, her voice rang out.

"There's a detail."

"What?"

"You triggered the wall at that location," she said. "It corresponds to the seventh column of the third section of the mural."

"So what?"

“That’s the starting point of the whole narrative chain,” she said, “and the only complete symbol that hasn’t been weathered away.”

Chen Hao stood up and walked to the wall. He looked in the direction she pointed. The markings in that spot were indeed newer than the others, as if they had been touched frequently.

"So... I didn't just randomly pick one?"

“You chose the touchpoints according to a certain logic,” she said. “You probably don’t even realize it yourself.”

"What do you mean? I have memories?"

"Or perhaps you remember it subconsciously."

"I can't even remember what I ate for dinner last night, how could I possibly remember a code from two thousand years ago?"

“Maybe it’s not you who remembers,” she said, “but your genes that remember.”

"Don't scare me with those kinds of words."

"I'm just proposing a hypothesis."

Chen Hao stared at the symbol for a long time. It looked like an inverted triangle with a horizontal line at the bottom, as simple as a child's doodle.

He reached out and touched it gently.

The moment my fingertips touched it, the entire wall emitted a low hum.

Nana immediately turned around. "Don't move!"

But the sound had already been made.

This time, there was no blue light, and no vibration. Only the screen of the probe ball suddenly flickered, displaying a new line of data.

“I received additional information,” she said.

"say what?"

She stared at the screen and read the sentence aloud.

"Welcome home, heir."