The Manchurian Railway, known as the South Manchuria Railway Company, was established by Japan in April 1906 in the Dalian area of Lushun, China. Since its establishment, there was the Manchurian Railway Investigation Department, and the first president of the Manchurian Railway, Goto Shinpei, called for the implementation of the "integration of military and iron", so that the Manchurian Railway Investigation Department was closely related to the Japanese military department, so it was also a veritable espionage activity, rather than a commercial cooperative exploration as it was called to the outside world.

In order to investigate the trade in the river basin, the spy department did not hesitate to spend a huge amount of money on the investigation, and even asked an investigator to go up the Yangtze River from Shanghai to Chengdu, which took one year and two months. At the same time, in preparation for the attack on the Soviet Union at that time, it took several years to compile the "Russian Military Gazetteer", and the investigation of the three eastern provinces can be called horror.

The Investigation Department took the team as a team and set out in batches from the three places of Fengtian, Xinjing, and Harbin at that time to conduct a so-called survey of the entire northeastern region, and at the same time to draw up the map and investigate the details of each village, how long it takes to walk from the city to the village, and how long it takes to drive. The number of people and households in each village, the number of people expected to increase in the next ten years, and even the number of production tools and kitchen knives in each household are recorded.

This shows how meticulous the so-called "exploration" of the Manchurian Railway Investigation Department, a spy agency, is.

And the wild frog ditch was accidentally discovered by the Manchurian Railway Investigation Department in 1941.

In 1939, the Japanese army was defeated at the Battle of Nomenkan, and realized that the Soviet Army was far stronger than they thought, so the northward strategy was canceled and the southward advance was changed to a south. At the same time, the Japanese army was more defensive against the Soviet army than before, so they overhauled fortified pillboxes on the northeastern border at that time.

However, it was impossible to deploy the entire northeast border, and at the same time, it was necessary to prevent the Soviet army from carrying out surprise attacks from "unexpected" positions, so the Manchurian Railway Investigation Department began to look for so-called loopholes in the defense line together with the people of the military department.

There are a total of 4 people in charge of the investigation team in the Wild Frog Gully area, namely the squad leader Masao Kabu, and the team members Jiro Koyama, Masashiro Kubo, and Shiro Izome.

Because of the squad leader, the name of this team is called Lusheng class.

The duty of the Lusheng class is to explore the loopholes in the area, in short, it is to worry about the Soviet army's plank road and the darkness of Chen Cang, after all, the Japanese army was most proud of the so-called surprise attack tactics at that time, and they were also worried that the Soviet army would adopt the same tactics, and they were even more afraid that when they woke up, the Soviet troops had appeared outside the barracks.

When Lushengban investigated Yewagul, Japan had already attacked Pearl Harbor, the United States had also declared war on Japan, and Japan was also eager to get mineral materials to support its own war, so Lushengban had another important purpose in exploring in this area, that is, to find oil.

But oil exploration is not an easy task, the Americans searched the desert for five years and finally gave up before discovering oil, while the Japanese have been searching for more than ten years after occupying the three eastern provinces without finding anything, which makes them very frustrated.

The reason why Lushengban wants to explore the wild frog gully, in addition to the strategic loopholes, is oil, because they know from the aborigines who used to be here that a black liquid can be ignited in the wild frog gully, and the black liquid can ignite, isn't it oil? Therefore, Lushengban rushed to the wild frog ditch as quickly as possible and began the exploration work.

But when they entered the wild frog ditch, they questioned the ecological environment here. First of all, this is a wetland, definitely not a foul-smelling swamp, but the presence of wetlands in the ravine is not very natural in the first place, and it stands to reason that the wetland should be more close to lakes and rivers.

On top of that, the wetland within the Wild Frog Gully stretches out on a mountain known locally as "Wanqi", which translates to Chinese as "unfrozen pond water".

It is also strange to say that when the deer class went, it was the most severe time in winter, and the water in the wild frog ditch was not frozen, on the contrary, there was temperature, after measurement, it was found that the water temperature was between 15 degrees and 25 degrees, which could not reach the temperature of the hot spring, but it was far higher than the general water temperature.

After monitoring the water quality, Lushengban determined that this is not a hot spring and there are no volcanoes around, but what caused it? This made them wonder and began to explore the wetland and the surrounding area.

When surveying the mountain wall at the end of the wild frog ditch, Lu Shengban found that the mountain wall also has a temperature, and it cannot accumulate snow, and the more you dig into it, the higher the temperature, and it seems that there is something else in the mountain wall.

On top of that, the discovery of the stones in the mountain wall that they mined would take about five hours for the temperature to gradually decrease, even if they were placed in the open air, led Lushengban to think that they might have found some kind of energy source that had never been found in human history.

As a result, Lushengban sent a telegram to the headquarters of the Manchurian Railway, providing their survey data.

At that time, the war in Japan was tight and it was not possible to draw too many manpower, but in order not to give up the so-called hope, a squadron was also sent to help.

At that time, the number of Japanese squadrons was about 200 people, and these 200 people were also temporarily transferred from various places, and there were even a large number of Korean soldiers among them, so it is enough to see that the Manchurian Railway and the Japanese military headquarters at that time did not attach much importance to this place, but only fulfilled the so-called due diligence.

When the group arrived at the Wild Frog Gully, they did not immediately set up camp, but began to excavate, first digging out what was inside, and who knew that after digging into it, they found the strange wooden planks with lines hidden in the mountain wall.

Although the textured planks felt wooden from the touch, they were surprised because they couldn't scratch, cut, or smash holes, and they used bullets and even explosives without any damage to the textured boards.

The people of the Lusheng class felt that this should be a major discovery, and the commander of the 200 people sent also felt that something was wrong, so he asked his subordinates to use local materials and build houses to prepare for the long-term exploration and research here.

At the same time, they did not relax their excavation, because of the relationship between the textured planks, so there was no need to be careful in the process of excavation, and there was no need to do further exploration, and they used blasting methods when encountering larger stones.

Therefore, in just one month, the cave in the state of the grid was dug out.

The appearance of the grid cave made the people of the Lusheng class realize that this was definitely not a natural formation, but the ancient humans did not have the technology to make that kind of grain plank, so they decided to continue digging deeper.

Eventually, they dug through the deepest part of Cave 5, and after the cave wall at its last collapsed, they discovered the endless darkness inside.

At the time, no one thought there was anything hidden in the endless darkness, just that it was a cave.

Therefore, 10 people were immediately sent into the cave to investigate, led by Izome Shiro of the Shikabu class, and for fear of getting lost, he also tied a rope around Izomeshiro's waist.

Soon after the 10 men entered the darkness, they could not hear any footsteps or see any lights shining on, and the people outside could only wait patiently.

But ten minutes passed, half an hour passed, these 10 people had no news, and when they dragged the rope, they found that no matter how they dragged it, they couldn't drag it out, and the original length of the rope was only 50 meters, and after connecting several other ropes, it barely reached 200 meters, and it stands to reason that Izoshi and others could only go 200 meters deep, and the rope was straight.

Moreover, the distance of 200 meters has already been reached in half an hour, and the most terrible thing is that when they drag the rope, they have dragged it for 250 meters, and they can still drag it out, just like someone has connected the rope for another 50 meters.

Because the rope was connected under the nose of the squad leader Masao Kasheng, he knew very well that there were only 200 meters, and what was the matter with the extra 50 meters? The people inside also did not carry extended ropes.

Masao Kabu began to test the extra 50 meters of rope and found that the texture of the rope was exactly the same as the rest of the 200 meters.

Kabu Masao didn't dare to delay, feeling that things were too strange, and motioned for them to continue dragging the rope out, and finally the length of the rope reached 500 meters, but even so, he still didn't drag out Shiro Izome, who was originally on the other end of the rope.

It should be something wrong, Shikabu Masao thought so, and then came up with a stupid solution, that is, let the rest of the people go inside one by one, and line up a longitudinal formation of 200 people in the cave, in order to detect how deep the cave is, if all 200 people enter the cave and still not reach the end, then return immediately.

Masao Kasheng's idea made the commander feel ridiculous and risky, but after all, it was the only stupid way, and he had to do it.

Then, under the arrangement of the commander and Masao Shika, everyone entered the cave one by one, one by one, and walked towards the endless darkness ahead.

Soon, all 200 people entered the cave, and after the last person entered the cave, he stood still, and Kabu Masao also signaled him to report the number by slapping and passing, and prompted the person in front to stop, and then asked the leader to start counting from 1 and return.

At first, the sound of the number could still be heard, but soon it was as if it had been swallowed up, and nothing could be heard.

Soon after, the number returned from the end, and it stands to reason that the last person at the mouth of the cave should have been a whole number of 200, but the person reported the number 210.

This result surprised Masao Kabu and the commander, obviously there were 200 people who went in this time, why did it become 210 people? Could it be that the 10 people from before were also in the team? It can't be, right? The cave was only so big, and it was straight, and if they had been discovered, the people inside would have reported it a long time ago.

Masao Kabu decided to report the number again according to the previous method, and the result of this report became 200 people.

This result did not make them breathe a sigh of relief, on the contrary, they felt even more strange, so they reported the number again, and this time the result of the report became 210 people.

The Japanese commander was annoyed, thinking that someone was joking, and strode in, asking for his own count.

The commander walked towards the depths of the cave, walking through the variables, and even carved the lines on the cave wall with a knife, counting one by one, and when he reached the innermost point, the number had reached 200, and there were still people standing there in front of him.

The commander stood in the position of 200 people, looking at the men who were looming in the darkness in front of him with their backs to him, and suddenly became afraid.

He looked at the 200th person next to him and asked, "Are you the first to come in?" ”

The man's reply was, "I forgot." ”