This airtight door is very large. Ke Lan estimated that it is nearly five meters high and more than two meters wide. The entire door panel is cast from a dark green alloy. An octagonal valve with a diameter of more than half a meter is installed in the middle of the door panel, and the metal handle is covered with rust.

Valves with purely mechanical structures are not common in the remains of the Alvin civilization. Most of their devices are driven by energy crystals, and even doors are no exception. The airtight door in front of Ke Lan is, on the contrary, closer to the design style of human civilization.

"Could this place have been modified by humans?" This thought popped up in Ke Lan's mind, but he quickly rejected it - not to mention whether anyone has ever entered this place, just looking at the degree of rust on this airtight door, it is estimated that this thing has been installed here for at least hundreds of years... and humans have only been on Alpha for fifty years.

"Hmm... a few hundred years is still too conservative. It must be tens of thousands of years..." Ke Lan poked the door panel with his finger, but found that his finger was instantly half sunk in - this dark green thing was not the original material of the door panel at all, but a floc-like substance similar to rust formed after the alloy was oxidized. As for why it has this color, it must be because the alloy formula contains a large amount of copper.

"But that doesn't make sense... The metal plates and metal frames used to reinforce the passages in other places aren't rusted that badly... Logically, the materials used for this door should be better than those in other places, so why is this door rusted so badly?"

Ke Lan hesitated for a few seconds before saying in a somewhat uncertain tone, "Could it be related to the thing behind the door?"

He glanced at the large characters engraved next to the airtight door - "First Level". From a semantic point of view, the interpretation of these Alpha characters should not deviate too much, but because of this, the information these characters can provide is extremely limited.

Do you want to open this door?

Ke Lan suddenly hesitated: when he pulled out the stalagmite from the corpse, he awakened the Seed of Erosion that had been in a state of suspended animation for decades; later, he pried off the ore on the stone pillar, causing seawater to flow back into the cave, and he almost drowned in the cave... This time, if he rashly opened the door, would something fatal happen again?

To be honest, Ke Lan is really a bit scared...

For a relic hunter, being timid is not necessarily a bad thing. As Lao Gou said, the brave ones would have died long ago, and only the timid ones can survive until now.

After thinking for a long time, Ke Lan finally decided to give up - his luck seemed to be a bit off today, and who knew what kind of monsters would be waiting for him behind this door. By then, it would be too late to regret.

Ke Lan took out a roll of tape, tore off a few pieces, and stuck them on the gap of the airtight door and the hinge at the other end, then continued walking forward.

The sound of flowing water above my head disappeared. It seemed that the seawater from the outside was no longer pouring in. After all the seawater entered the reservoir, the cave above would be passable.

However, Ke Lan did not plan to go back up there. After knowing that the Alpha people's drainage system had the ability to deform at will, the original "underground maze" was directly upgraded to a more difficult "moving maze". Even if Ke Lan had the design drawings of the drainage system's construction, he might not be able to get out of it - after all, no one could predict when the water flow channel would change, and he knew nothing about the causes and purposes of the changes.

In comparison, this cave, which may be a "maintenance passage", is much more stable.

…

After walking another four pieces of chalk, Ke Lan was forced to stop.

There was another landslide, but this time there was not even a crack left. A large amount of rubble blocked the passage tightly. Even the snake-like robot specially used to explore small pipes could not get through.

The only tool Ke Lan had was a folding pickaxe he found in the camp of Team 776. Given his physical strength, it would probably take him a whole day to clear away a meter of rubble.

The previous landslide passage was about seven or eight meters long. If this section was also that long, Ke Lan would have to spend a full week digging it.

Moreover, the further we go, the worse the situation in the tunnel becomes, and such landslides are expected to increase more and more.

"Alas." Ke Lan sighed helplessly, "It seems that I still have to go through that door."

After leaving a mark at the landslide site, Ke Lan had no choice but to turn around again.

Following the line drawn in chalk on the wall, he returned to the huge airtight door.

The tape used as a seal on the door was intact, which made him feel relieved. According to the common plot in horror movies, the tape should have been torn by now, and there would be a figure hiding in the darkness...

However, this kind of plot is not uncommon in the ruins of the Alpha civilization... Ke Lan has read many tomb-robbing novels from the old era. Compared with the high-tech traps of the Alpha civilization, the mechanisms in those ancient tombs can only be regarded as child's play. And things like dumplings and ghosts are even more dwarfed by the seeds of erosion.

"...This valve...is really high..."

Ke Lan stood on tiptoe and stretched her arms as far upward as possible, but she could only barely grab the lower edge of the valve and was unable to turn it at all.

"It seems that the data published in the official documents are quite accurate..." For the Alpha people who are about 2.5 to 3 meters tall, the size of this airtight door is actually not exaggerated, and the height of the valve is just right, but for humans, it is a bit troublesome.

There was no other way, Ke Lan could only hook the valve with a pickaxe and turn it little by little by pulling it down continuously.

There was a teeth-grinding sound of friction between metal and large pieces of dark green oxide fell off... Fortunately, the mechanical structure inside the valve was still intact. When pulling the valve, Ke Lan could even clearly feel the force of the gears meshing with each other - if these gears were as rusty as this door panel, there would probably be only one valve spinning there, and even if Ke Lan turned it hundreds of times, he might not be able to open the door.

“Click.”

A crisp sound came from inside the airtight door, followed by a continuous sound of metal collision. Ke Lan waited for thirty seconds before the crack of the airtight door "popped" and a tiny gap opened.

The door opened.