Although we had chosen a relatively gentle slope to ascend the mountain, our climbing speed was still very slow, mainly because our backpacks were too heavy.

Fatty said, "Just adapt. It'll get easier as we go."

Sure enough, as Fatty said, as we walked, our bodies gradually adapted to the weight, and the discomfort gradually disappeared.

The route we had planned avoided dangerous peaks, opting for a gentler but longer path. It would take more than ten days to reach our destination from the starting point, and with the return trip, our supplies were only enough for a month at our destination.

Initially, the mountain path was lush and verdant, but as the altitude increased, the green vegetation was gradually replaced by white snow-capped mountains. During the ascent, Han Yu experienced altitude sickness. Fatty quickly took some of Han Yu's load onto himself and gave Han Yu extra food during meals. We also quickly used the oxygen concentrator for Han Yu, slowed down our pace, and increased the number of rest stops. Han Yu slowly adapted, but still looked sickly and listless.

After ascending the mountain, we changed to two meals a day, one when we woke up in the morning and one after setting up camp at night. Because fuel was limited, we basically didn't light a fire. We ate either self-heating food or easily portable quick foods like compressed biscuits or chocolate. Our tent wasn't big. Once the four of us crawled into our sleeping bags and lay down in the tent, almost all the space inside was taken up.

On our way to our destination, we encountered two snowfalls, forcing us to camp and rest in place. Fortunately, we arrived at our destination on schedule. Han Yu, who seemed to have been holding her breath the whole way, collapsed completely the day after we arrived, developing a high fever. Fatty quickly took out the fever reducers and antibiotics we had prepared for emergencies, melted snow water, disinfected it, boiled it, and gave it to her. Han Yu only improved after two days of rest.

Our campsite was about a kilometer away from Devil's Col. Across Devil's Col, on the opposite side, was the z organization's scientific expedition team's camp. Because we had chosen a relatively high position for our camp, we could easily observe their every move. At the same time, our camp was shielded by the mountain, so they couldn't detect us.

It was a case of 'the enemy is in the open, while we are in the dark'.

Because Han Yu was sick, and we were exhausted from our forced march, we did almost nothing for the first two days after arriving at our destination, mainly taking turns resting. Only after we had rested did we begin to observe the z organization's scientific expedition team and Devil's Col.

Devil's Col didn't seem special from the outside; it was just a depression between two snow-capped mountains, a patch of white snow with a few exposed rocks and soil. However, according to the top-secret information Zoe had brought, Devil's Col actually had boundaries, which seemed to be changing. However, because of some kind of interference (the z organization's data called it magnetic field interference), electronic equipment would suddenly malfunction when approaching Devil's Col. I tried to use a simple drone I made to measure the boundaries of Devil's Col and film its internal environment.

Fatty had brought two military-grade high-powered telescopes, so any movement in the z organization's scientific expedition team's camp could be clearly seen. It took Zoe and Fatty several days to figure out what the expedition team was doing.

On the fifth night after setting up camp, it started snowing again on the mountain. The good news was that Han Yu's fever had broken, and her physical condition was slowly recovering. After dinner, we used a hand-cranked generator to power the small light bulb hanging in the center of the tent. The light was dim and weak, barely illuminating this small space, and we huddled in the tent to discuss our discoveries over the past few days.

Zoe and Fatty had discovered that there were a total of twelve people in the scientific expedition team's camp, nine of whom were expedition members. They were divided into three groups of three, and acted as a unit. Of the other three people, one seemed to be the leader, and the other two seemed to be guards.

In the last two days, the expedition team's supply personnel had brought several dogs up from the mountain, suggesting they were planning something.

I had used the drone to explore the boundary of Devil's Col facing our side. The boundary of Devil's Col had changed compared to the boundary measured twenty years ago in the data, but this change seemed to be irregular, like a liquid. Overall, Devil's Col seemed to be flowing and shifting towards the z organization's scientific expedition team's camp. Unfortunately, the drone always lost power when approaching Devil's Col, so the recorded video was intermittent and blurry.

Han Yu seemed interested in my findings. After I finished describing them, she wrote and drew on paper, pausing occasionally to look up and ask me a question: "When you were measuring the boundary, what was the state of the drone the moment it touched the boundary?"

I replied, "When the drone touches the boundary of the col, there will be a remote control failure and power outage. But I tied a fishing line to the bottom of the drone. The moment it loses power, I desperately reel in the line. As soon as it leaves that area, everything returns to normal, the power supply is normal, and the remote control works fine."

I recalled the scene when I was flying the drone and added, "...But the drone doesn't seem to actually touch the boundary of the col, because as long as it approaches Devil's Col to a certain distance, a power outage occurs, and it falls vertically. What's strange is that the drone doesn't fall in the direction of flight due to inertia. I can't figure that out."

Han Yu nodded thoughtfully, then continued to write and draw on the paper.

The next morning, Fatty and Zoe went to scout early in the morning. When Han Yu woke up, only the two of us were left in the tent.

Han Yu only ate a compressed biscuit for breakfast, then left the tent. She found a few flat stones near the camp, about the size of a watch face. She tossed them in her hand and felt that the weight was just right. I didn't know what she was going to do with the stones.

Han Yu took the camera and the stones and walked towards a place. I was afraid that her health was not good and that she would encounter danger again, so I silently followed her.

The place Han Yu went to was a low mountain peak on the side of Devil's Col. The opposite of the mountain peak was the towering mountain peak on the other side of the col. The two peaks were hundreds of meters apart, and the land between the peaks was Devil's Col. The place where Han Yu and I were standing was dozens of meters higher than where we were camped, very close to Devil's Col. It was a platform on the snow mountain.

Han Yu suddenly asked me, "Can you skip stones?"

"Of course, my highest record is more than ten skips!" I replied confidently.

"That's good..." Han Yu put the flat stone in my hand, then picked up the camera, opened the lens cap, turned it on, pointed it at Devil's Col, and said, "I'll point you in a few directions later, and you use the technique of skipping stones to throw the stones out with all your strength."

Han Yu pressed the camera's record button, pointed to a certain position in Devil's Col, and said, "Throw it there. When you throw it out, you must make the stone rotate at high speed."

The place Han Yu pointed to was relatively far away, estimated to be nearly a hundred meters. If Fatty was there, he could definitely throw the stone accurately to the target position easily, but I might not be able to.

I mustered all my strength and threw the stone out with a "swoosh"~ sound. The flat stone flew like a small flying saucer, rotating rapidly, and accurately threw it to the place Han Yu indicated. I saw the stone flying to a certain height directly above Devil's Col, and then it suddenly disappeared.

I suddenly realized that Devil's Col had a height.

Han Yu asked, "Did you see the place where the stone disappeared?"

I nodded.

Han Yu continued, "This time, you pretend that the place where the stone disappeared is the surface of the water. When you throw it, increase the spin speed and initial speed, just like skipping stones."

Then, Han Yu took me down a distance to reduce the height of throwing the stone, trying to get closer to the upper boundary of Devil's Col, so that we could reduce the speed of the stone falling and ensure that the angle of attack was less than 30 degrees, which is also the technique for skipping stones far and getting many skips.

I used all my strength to throw the stone out with all my strength.

Something strange happened. The spinning stone "skipped" a bit at the place where it was about to disappear, with a slight upward movement, and then flew to a farther place before disappearing, just like skipping stones.

I stared at Han Yu in amazement.

Han Yu didn't turn off the camera's recording function. She signaled me to throw all the remaining stones. I threw all the remaining stones out one after another. Maybe it was because I didn't have the strength, but the stones behind didn't fly as far as the second stone, but I could clearly feel that the stone had a brief pause of about one second before disappearing.

After throwing the stones, Han Yu put away the camera, and we returned to the camp together.