In the dim and cramped secret passage, Yu Bin walked silently alone, leaving some marks on the rock wall beside him from time to time.

This secret passage deep in the Spider Courtyard is very ancient, and in many places it has even collapsed in small areas due to a long period of unmaintained, or has been penetrated by some unknown underground plant roots, forming a thick barrier.

Yu Bin had no choice but to look for those shallower secret passages as much as possible, although that would increase the probability of encountering dark elves, but compared to those ancient, deeper underground secret passages, these shallow secret passages were more accessible and well-maintained.

Many people think that the underground world is on the same plane, just like the world of Entagre, but this is actually a misconception. The root of this perception is that players don't get enough information in the Underworld to calculate their spatial location.

In addition to those dangerous underground creatures, the dark underground world is more deadly misleading to the senses, in this environment, your judgment of direction, time, depth, height and so on will drop to a very low level, or even completely lose your grasp of them. You may think you're going in the same direction all along, but you're probably going in circles.

Even many times, you can't feel like you're going uphill or downhill, and it's possible that you'll walk through a long passage and arrive at your destination just a few hundred meters below your starting point.

The same is true for the distribution of cities in the underworld, they are not on the same level at all, and the two cities are probably separated by less than a kilometer (in height), but the underground passages that connect them are likely to be hundreds or even thousands of kilometers long.

What's worse is that the large number of forks in the underpass makes these passages form a natural labyrinth, the figure 8 can only be regarded as the foundation, the nine-square grid is even more common, and in the previous life, someone even found a three-dimensional labyrinth that stretches for thousands of kilometers and has a total of five floors.

Even the system has set up a special achievement for this purpose: [Walking in the Underworld]. The only requirement to complete this achievement is to reach another on foot from any of the underground cities, exploring at least six complete underground passages along the way.

There are two similar achievements: Opening the Door to the Void of Chaos and Exploring the End of the Abyss. The former requires the player to open a portal to the Void of Chaos and then go inside in a circle to return from another portal. The latter, on the other hand, requires the player to find a random pit in the first layer of the Abyss and jump into it, and if they can come back alive, they can complete this achievement.

This is the challenge activity called "Triathlon" by players in the previous life, and the veteran players have given each of these three achievements corresponding names, walking the way of the underground world, kicking the door of the chaotic void, and jumping into the pit of the bottomless abyss!

Players who can complete these three achievements don't even need any preconditions to get a very awesome profession: [World Explorer], this class can exist at the same time as other classes, does not provide any attribute and skill bonuses, but can allow players to have the ability to freely enter and exit various worlds, whether it is the bottomless abyss or hell, the elemental world or the chaotic void, you can wander around, just like entering your own home!

Of course, no one will take risks for such a profession, the underground world is fine, but the chaotic void and the bottomless abyss are not safe places, the former will randomly throw players to other worlds, and if you are unlucky, you will not even be able to return for a lifetime, and the latter is even worse, there is a great possibility that the pit leads to the lair of some abyss lord, and you can only stay there as a pet for the rest of your life!

I don't know how long I walked, but when Yu Bin finally heard the faint sound of running water, he was sure that he had finally found the right direction.

Moving on, the exit of the secret passage is on a cliff, and below the cliff is an underground river, and the roaring river goes around the cliff and continues to advance, and it is not known where it eventually leads, perhaps some cavern located deeper underground.

If Yu Bin remembers correctly, heading upstream of this underground river, he can reach Lake East Niagarton, which is nothing more than a reservoir through which this underground river passes, and no one knows its source.

This place is located more than 280 meters underground in Mosso Black City, and the cliff where Yu Bin is now is actually the rock wall where Mithril Castle sits, but the height difference is nearly 400 meters.

Look, the underworld is so magical!

Sure that he was not going in the wrong direction, Yu Bin began to look for a secret passage to the Mithril Hall, and soon he found an ancient secret passage exit on the other side of the cliff, which was more than five meters high alone, and the stone walls were covered with various mosses and ferns from the underworld.

The secret passage dug by the drow elves themselves will never be so huge, the height of those black skins is generally not more than two meters, digging a five-meter secret passage is simply an act of taking off your pants and farting, the only explanation is that the digger of this secret passage is an underground race under the rule of the black dragon queen Synestra.

It is also the only secret passage at this height that can pass through the huge black dragon and those special underground races, such as the Shadow Three-Headed Dog.

And the other end of this secret passage undoubtedly leads to the Mithril Hall!

When entering the secret passage, Yu Bin subconsciously turned his head to look at the underground river under the cliff, a weird smile appeared on the corner of his mouth, and then walked in without looking back.

A few minutes later, a figure slowly rose on the rushing river, it was already dark, but this figure was darker than this darkness, as if no color could leave a mark on his body. The figure looked at the entrance of the secret passage for a few minutes, then re-entered the river and disappeared.

On the other side, Yu Bin continued to move along the secret passage, and it could be seen that the craftsmen who excavated this secret passage did not simply use it as an escape route, and some rooms would be set up at certain distances in the secret passage, and traces of various materials and furniture could be seen in the room, and even some pieces of equipment remained on the ground.

The secret passage is not a straight line, but is divided into sections of compartments of different lengths, each of which is connected by a ninety-degree corner, which Yu Bin guesses is likely to defend against those who enter the secret passage, and each corner can be used as a line of defense.

It can be seen that in the era when Sinisterra ruled the underworld, defending against the invasion of the bottomless abyss was a matter of life and death, and the threat of those abyssal demons was so great that they did not hesitate to build the secret passage of escape into a fortification to meet the enemy.

The height difference was nearly four hundred meters, but Yu Bin estimated that the length of the entire secret passage was even more than ten kilometers along the way, and it was hard to imagine how much it cost those fallen dwarves and craftsmen of various races to dig this secret passage.

The end of the secret passage is located in the depths of the arsenal on the third basement level of Mithril Castle, which was once used to store various war supplies and weapons and armor, but since Rose betrayed Sinestra, the entire underground three floors have been completely sealed, and no one has used this secret passage again.

And time passes, after tens of thousands of years of strife and civil strife, no one inside the dark elves knows that there is such a secret passage enough to pass through the army under the Mithril Castle, otherwise, Kareth doesn't even have to waste time storming the platform, as long as she follows this secret passage, she can easily enter the inside of the Mithril Castle and directly occupy the second underground floor where the core magic array is located.

As Yu Bin's destination, the Mithril Hall is located on the first basement floor, just above the core magic array, and there are only two ways to enter the Mithril Hall, either by going down the stairs from the first floor, or by going up from the place where the core magic array is located on the second basement floor.

Either way, it's not easy. Yu Bin didn't know how far the war was going outside Mythril Castle, and it was Kareth or Elvia who won? If it was the former, he must have been eager to leave Mithril Castle with all his troops at this time, and go to Mossoblack Town to suppress the rebellion and restore his rule, and it is likely that only those civilian servants who have no combat effectiveness will remain in Mithril Castle. And if it's the latter, Yu Bin may have to think about how to explain his appearance here!

The worst thing is that the two sides are still in a state of fighting, and the flames of war have spread to the entire Mithril Castle, and when he thinks that the corridors and rooms above are full of dark elves fighting each other, Yu Bin feels that his small body can't support the Mithril Hall at all.

The corridor leading to the second basement floor has been completely demolished, and even the gate is sealed by rocks, but this is difficult for Yu Bin, such a large castle must have perfect ventilation facilities, otherwise the lack of air alone is enough for the dark elves living in it to suffocate to death. And when Rose closes the entire underground three floors, she will inevitably leave these ventilation facilities, after all, every ventilation pipe, one in and one out is a reasonable shot, and if one end is sealed, this ventilation system will be considered useless.

After looking for a while, Yu Bin finally found the ventilation hole hidden in the huge column, and used the rune sword in his hand to dig a hole in the pillar that was enough for him to pass through, and along the ventilation pipe, Yu Bin found that Rose did not completely close the ventilation pipe, but only set up a few iron fences between the pipes on the third and second floors.

These fences forged from ordinary iron bars were useless in front of Bin's weapons, and after easily destroying them, Yu Bin followed the ventilation duct to the second basement floor.

Listening closely, Yu Bin didn't notice the sound of fighting outside the pipe, it seemed that either the war had been decided, or the two sides were still stuck outside Mithril Castle.

Yu Bin carefully dug out the vent and drilled out, the entire second underground floor was dark, there were no torches, and there was no magic lighting, which made Yu Bin feel very strange, could it be that the battle situation outside was so dangerous that Gina Fei even withdrew the servants here to fill the defense?

However, this is a good thing for Bin, he has decided to go to the central control room on the second basement floor where the core magic array is located first, if there are still guards there, he has to give up and take a risk to detour to the first floor to go to the Mithril Hall.

After walking a few steps, Yu Bin suddenly tripped over something, and he subconsciously jumped back, the rune sword in his hand was horizontal to his chest, guarding against possible traps or attackers.

But nothing happened, and no soul fluctuations were perceived in the soul vision, as if the entire Mithril Castle had lost its vitality.

The silence and darkness can almost drive people crazy, Yu Bin didn't dare to let down his vigilance, he thought about it for a while, and finally chose to light the magic torch in his backpack.

The flame ignited, the light appeared, and what was revealed in front of Bin was a hell on earth!

On the ground, in the corridors, next to the statues, and in the rooms, there were corpses everywhere, including drow elves, dark goblins, fallen dwarves, and even some forest elves and snow elves dressed as servants.

Traces of battle were everywhere, broken weapons and broken armor were everywhere, and stumps and broken arms were scattered all over the floor like promotional activities. The blood covered almost the entire ground and was close to coagulation. Obviously, it has been a long time since the tragic battle that caused all this, and Yu Bin speculated that it would be at least two hours.

This is normal, there is no way to determine the passage of time in the secret passage, although Yu Bin has been silently counting the seconds in his heart, but that cannot be used as a basis for judging time.

Cautiously stepping over these corpses, Yu Bin found the central control room on the second basement floor where the core magic array was located, the door of the control room was opened, and the Drow elf guard wearing heavy armor had turned into corpses, and fell miserably in front of the door, it seemed that he was hit head-on by some kind of powerful magic, and the small half of his body was almost beaten into a meat patty, and the corrosive effect caused by the shadow element could be seen on the torn wound.

The control room was in shambles, the magic array on the ground the size of half a football field had been completely scrapped, and the magic lines had been cut by several thick sword marks, leaving only the remaining magic power occasionally emitting a glimmer of light of different colors. On the walls around the control room, traces of wanton sword qi could also be seen, and Yu Bin could even feel how the attacker was wielding the long sword in his hand here.

On the side of the control room, the staircase leading to the Mithril Hall has been completely destroyed, and the closed door is covered in sword marks.

Mithril Hall, as the name suggests, this room is made of high-purity Mithril poured out of its entirety, even this door, although the sword marks on the door look terrible, but obviously did not cause fatal damage to the door, the attacker obviously could not enter the Mithril Hall in this way!

Since this is not possible, the only thing left is the gate from the other side of the first floor.

And Yu Bin is also very curious, how is the war going outside!