The Lower Chamber
Long Tian squatted on the deck for a while, reviewing the characteristics of the rhythmic vibrations in his mind. Its frequency wasn't high, but it was very steady, like the vibrations produced by some fixed structure in continuous operation. He stood up and walked to the stern, saying, "I'll go down again, this time with a rope. If the vibrations are coming from under the pavement, there should be a cavity underneath; we need to find a way in."
The man at the stern took a roll of thin rope from the cabin and handed it to him, tying one end to an iron ring on the side of the boat. Long Tian tied the rope around his waist, flipped into the water, and swam back down the same route he had just swum to the wider crack. The light of the Dragon Shadow spread out in the murky water, illuminating the edges of the crack and the fine horizontal cracks on the surrounding paving.
He crouched at the edge of the crack, letting the aura of the Origin Return Pearl extend downwards along its interior. Near the bottom, he encountered a medium different from the paving stone. It was denser and slightly warmer, as if it had been continuously heated and maintained at a constant temperature. He traced his aura along the surface of this medium and discovered that it had formed a smooth layer directly below the crack, beneath which lay the source of the vibrations. He placed his palm on the stone surface at the edge of the crack and probed along the edge of the layer, finding a relatively large opening near the fork at the end of the crack—just wide enough for a person to pass through sideways.
He untied the rope from his waist, tied one end to a protruding stone edge at the edge of the crack, and left the other end behind him as a guide for the return journey. After making sure it was secure, he turned sideways and squeezed into the crack.
The interior space, separated by the paved layer, was wider than he had expected, like a chamber sandwiched between two structural layers. It was about an arm and a half high, with the top being the bottom of the paved surface and the bottom being a dark gray structural layer. The sides extended into the distance, their edges invisible under the illumination of the Dragon Shadow. The source of the continuous vibration was deep within the chamber, emitting stable low-frequency pulses from a fixed location.
Long Tian walked forward along the plane at the bottom of the chamber for a while. The ground remained stable despite the vibrations, not loosening due to the rhythmic tremors. After walking about ten steps, a vertical tubular structure appeared on the ground ahead, extending from the bottom to the bottom of the paved surface above. The surface of the tube was covered with a dark metallic coating, and the vibrations were emanating from inside the tube. He moved closer and saw several fine longitudinal grooves on the outer wall of the tube, with a grayish-white light shining through the bottom of the grooves. The light flickered in sync with the rhythm of the vibrations, as if some of the energy flow inside the tube was being released through the grooves on the outer wall as it passed through.
He crouched down beside the pipe and placed his palm on its surface. The aura of the Origin Return Pearl spread along the pipe wall, partially absorbed at the narrow grooves, and conducted downwards along the internal paths of the grooves, entering a deeper layer. He sensed the direction the aura was probing downwards and discovered that the bottom of the pipe connected to a wider base structure, with multiple branch pipes extending outwards from the pipe, like a basic pipe network distributed beneath the entire paved surface. The direction of the pipes corresponded perfectly to the arrangement of the guide channels on the paved surface, like two layers of the same system.
He walked around the edge of the tube and found a low door perpendicular to the tube wall on the other side. The door was made of metal, with no handle or keyhole, only a circular mark embedded in the center, the same size as the mark plate that Long Tian had seen on the chamber wall earlier. There was a vertical line in the center of the mark, the same outline as the vertical line on Dragon Shadow's forehead. He placed his palm on the mark, and after the aura of the Origin Return Pearl was introduced into the mark, the door slid open along its center line, revealing a space inside the tube. Inside the tube was a vertical conduit, extending from the bottom upwards, straight to the bottom of the paved surface. The inner wall of the conduit was smooth, and a continuous layer of light flowed on its surface, pulsating synchronously with the vibration, forming a stable upward flow of light inside the tube. Long Tian squatted at the entrance of the tube for a while, memorizing its structure and operation. After confirming that there were no abnormalities or blockages, he stepped out through the low door, closed the door again, and walked back to the exit at the edge of the crack.
When he returned to the outside of the paved surface through the crack, his breathing was a little heavier, but the rhythm was steady. He untied the rope tied to the stone edge, floated back to the surface along the way he came, climbed onto the boat, squatted on the side of the boat to wipe the water droplets off his face, and sat on the deck to explain in detail the internal structure and operation of the pipe.
After listening, the person at the stern secured the rudder, squatted down by the gunwale, and looked at the area below the water where fine debris was still continuously emerging. He said, "That pipe network has been operating continuously, supplying energy from the internal structure to each branch. The cracks in the outer layer of the pavement are due to fatigue caused by long-term vibration of the stone above the pipes. To stop the spalling, the energy flow inside the pipes needs to be temporarily cut off, preventing the stone layer above the network from being continuously subjected to vibration, and then reinforcement should be done on the outer cracks."