Xia Lei’s left eye went to the sound as soon as he heard it. His eye saw through the grass, and saw the thing in the grass. He couldn’t help laughing to himself — what had been hidden in the grass was not a person but a snake.

It was a false alarm.

Xia Lei moved forward, going around the area with the snake. He came to the foot of the mountain about ten minutes later and finally saw that tombstone. It was hidden in the grass, and only half of it was left. The thick grass had covered it up, and the broken surface was covered with bird droppings. The part which had broken off had fallen in the grass to one side of it, and faint markings of a cross could be seen on it. The stone had moss crawling all over it, and people had carved graffiti in Italian on the surface of the stone — Alice was here, I love Leonardo, Peter is an idiot.

It seemed Italians liked to do these sort of things too.

These bit of vandalism also proved one thing, and that was that this place was remote, but people still came here. The tombstone might even have been broken because of these visitors.

A mound of dirt lay behind the tombstone. It wasn’t very high, perhaps up to a person’s knee. The mound was covered in wild grass, and bird nests of birds which nested on the ground. There was nothing special about this place other than these things. The initial impression was that this was just a normal grave. No noble was buried here, and it was most likely someone who had been a carpenter, a butcher, a farmer, or someone completely ordinary.

But Xia Lei grew excited when he first saw this ordinary-looking grave. It looked almost 90% similar to what had been painted.

Hundreds of years had passed, and this grave had had a big change, but the mountain and the river opposite matched the painting exactly. If he took the cross on the tombstone into consideration, the matching percentage increased further.

‘The map which da Vinci had left on the canvas was fairly complicated. It was like a maze. The entrance to that was below this tombstone. It looks like I really have to dig up a grave. I’ll have to take a look underground before I start on that,’ thought Xia Lei. His left eye twitched after he thought that, and activated his X-ray vision.

The dirt slowly disappeared from his vision, and when he was about 1.5 metres in, a large marble slab blocked his X-ray vision. He tried to see through it, but alas, he could go no further than halfway through it. 1.5 metres of dirt and partway through a marble slab was the limit of his X-ray vision.

Everything had its limits, and his X-ray vision was no exception. If he had no limits, he would have been able to see what was happening on the other end of the world, or even see the surfaces of planets far away. This was an impossible thing.

He did not manage to see further, but that marble slab was a clue in itself. There had not been a coffin but a large marble slab. This was obviously a fake grave, and its secret lay below that marble slab.

Xia Lei looked around himself. It was quiet. He did not see anyone else around either. This situation suited him perfectly. He removed his backpack from his shoulders and took out a shovel to start digging.

The grave dirt was very soft, and loose. It was not difficult for him to dig at all. He dug and he dug, and the pit before him grew deeper and deeper. The pile of dirt behind him grew taller and taller.

One hour later, the buried marble slab was exposed to the air. It was much larger than the pit he had dug. He used his X-ray vision on the area around it, and quickly discovered that this marble slab was like a door which had been placed in the dirt. What made his heart sink a little, was that this marble slab was startlingly thick. He would not be able to see through this slab even if he stood on it and tried his best to see through it with his X-ray vision.

He estimated that this marble slab was at least a metre thick, and was over a hundred tons in weight!

This conclusion surprised himself. There had been no tools for the people of hundreds of years ago to move a marble slab over a hundred tons to this place, but here it was. Unbelievable.

‘Damn it. How am I to go down with such a big marble slab in my way?” Xia Lei was perplexed.

The simplest way was to blast it with explosives but the quake from the explosion was a bad thing. It would attract the attention of the town’s residents, and also bring the police. However, if he did not use explosives, there was no way for him to move it aside even if he was the strongest man on Earth.

Was this a dead end?

Xia Lei frowned. His gaze went to the marble slab again. The white corner of something sticking out of the dirt caught his eye, and he squatted to wipe away dirt with his hand.

Hidden in the dirt was a round ball carved out of white jade, about the size of a basketball. Half the ball was embedded in the marble slab, and he saw a pit below it when he lifted it. There was a gear in the pit. The gear was made out of bronze, but the strange thing was that the gear teeth were not a normal ones, but in the shape of letters.

‘What sort of mechanism is this?’ Xia Lei was filled with curiosity. He pushed at the gear with his hand. There was heavy resistance, but the gear still moved a little. The letter B on the gear tooth slid into a part of the marble, and became two-thirds of a B.

Xia Lei then pushed the gear again, towards the marble slab. New letters appeared, one by one, and the resistance lessened with each letter. A few minutes later, he had cycled through all the teeth of the gear, from B to B. The marble slab did not open up, however, and there was no secret door to open either. This gear was like some intelligent joke, used to prank adventurers.

‘That’s can’t be it. I must have missed something.’ Xia Lei pondered for a bit, then pushed the gear through one cycle again, from B to B. There was no further movement this time either.

Then Xia Lei was struck by a thought. He immediately looked at the opposite side of the gear and his left eye twitched. The dirt covering up the marble disappeared from his vision. He spotted another white jade ball which looked exactly the same as what he had picked up earlier.

Xia Lei walked over eagerly. He cleared the dirt away then picked up the ball. As expected, the bottom of the ball had a small pit too, and a bronze gear. What was different was that the first letter on the first gear was B, and the first letter on this one was W.

Xia Lei pushed the gear, and it moved from W to W. The marble slab did not move at all.

These two bronze gears were obviously the opening mechanism, and the letters were the key to using this mechanism. However, he had tried all of the letters… Why was there still no movement?

He thought and he thought, and he suddenly thought of Leonardo da Vinci’s Mona Lisa. In that instant, he seemed to understand something, and a faint smile appeared in the corners of his lips. He then walked to the first bronze gear, and pushed the letter A to the top. He then went to the second bronze gear and moved the letter E to the top.

Clank clank clank…

A strange sound was heard, and the marble slab beneath his feet started to shake.

The letters A and E had been the code to unlock the marble slab! This answer had been left by da Vinci in the smiling eyes of the Mona Lisa!

The shaking grew more intense, like hundreds of thousands of gears were moving to shift the heavy marble stone slab.

Xia Lei did not dare to stay on the marble slab. He jumped up the pile of dirt. The marble slab opened up with a boom just as his feet touched the dirt. An opening two feet wide appeared. Xia Lei then discovered that it had not just been a marble slab, but two slabs put together. The craftsmanship was so exquisite that he had not been able to see any gaps between the two slabs.

The two marble slabs and pushed into the dirt on either sides of the pit, and a bit of dirt fell into the opening with a rustle. Xia Lei backed a short distance away, and peered down into the opening between the marble slabs.

The space under the marble slabs was an inky darkness, and the light he shone into it seemed to have been swallowed by the darkness. He could not see what lay at the bottom at all.

Xia Lei activated his power again, and his left eye saw through the darkness, searching through the dark, down, down. He saw the bottom now, and it shocked him. The space under the marble slabs was not really very deep, but the bottom of it was piled high with bones. Bones of humans, bones of animals, whichever bones they were, they had been painted black. The light he had shone down earlier had actually reached the bottom, but the large number of black bones had made some sort of black “whirlpool” which made it seem like that light had been swallowed.

It wasn’t just the bones which were black — the stone walls under them were blacked too. Black bones, black walls… The space under the marble slabs was a black world, and looked like it could swallow everything, not even letting ray of light escape.

Xia Lei abruptly remembered Princess Yongmei’s description. She had been closed up in a world of darkness. No sound, no light, no warmth, nothing. She did not want to stay in there, not one second.

‘This design… Did Leonardo da Vinci also study the space in the box? He knew more than me?’

No matter what it was, he was here now. It was a terrifying place, but he had to go down and investigate.

A few minutes later, Xia Lei used the rock-climbing gear in his backpack to slide down to the bottom. He stood on the pile of bones, and could see the gap between the marble slab above, as well as the faint light which came from that gap. It was just 20 metres from the bottom to the surface, so it was not a bottomless pit. He also quickly discovered that the paint on the bones and the stone walls was not ordinary paint, but a paint which could absorb light.

Crack! Xia Lei lit up a light stick. Using the light from it, he quickly found an entrance hidden behind a stone wall.

The passageway stretched on. The stone which made up the passage had also been painted black. He could not see the end of the passageway just by looking at it. This passageway was well and truly terrifying.

While Xia Lei was observing the passageway, the marble slabs above his head shut with a boom.