The door blocked off everyone and protected the secret within it, making it an obstacle hard for outsiders to overcome.

Correspondingly, they would be able to utilize the door’s characteristics to their advantage if they could conquer the building and claim it as theirs.

It was sturdy and durable.

An equivalent to an underground fortress to hide inside when in dangerous situations!

However, there was a premise for this to be true.

They had to make their way into the building before they could think about its future uses. It would be useless for them to overthink it while still being blocked outside by the door.

Li Hu was amazed as he thought about the possibilities and finally nodded in agreement.

After receiving the green light to proceed, Liu Cheng returned to the door and began to instruct the other three to take out all sorts of bottles and jars from their tool boxes.

These things were various fluids that the four had made during their spare time.

Red, green, blue, and purple.

The different colored solutions began to be mixed into one bottle, and a jet black solution began to spread out from the center of the solution, gradually engulfing the other colors after a few vigorous shakes by Liu Cheng.

“It’s ready!”

After shaking the bottle for five minutes, the solution turned pitch black and slowly transformed into a colorless and transparent solution.

Liu Cheng exclaimed in excitement and halted for a moment.

Half an hour had passed since three in the afternoon, and the time had begun to get closer to sunset.

Liu Cheng did not dare to delay further and immediately strode toward the door with the solution in his hand. Immediately, he carefully poured the solution onto the door’s lower right corner.

Hiss…

The colorless, odorless solution seemed harmless to humans and animals.

In actual fact, the moment it touched the door, it was like sulfuric acid corroding white paper, and a scorching odor immediately spread out from the reaction upon contact.

Instantly, the lower right corner of the door began to change in color. Countless holes appeared, which would trigger one who had trypophobia upon seeing it.

“Quickly prepare the A-3-552 solution!”

Liu Cheng glanced at the door in dissatisfaction and quickly ordered the other three to continue swiftly mixing another solution.

Although the solution was able to corrode the material used to construct the door, the damage that was done was irreversible.

They would have to make a few tons of the solution to pour on the door, corroding it layer by layer if they wanted to use this method to open the door.

It was not realistic, nor was it worthwhile!

Five minutes later…

Holding the newly prepared colorless solution, Liu Cheng approached the lower left corner of the door and continued pouring the solution onto it.

This time, the reaction speed was significantly slower when in contact with the door’s material. Although the smell was still pungent and unpleasant, the material could be preserved, and no large area of corrosion occurred.

“It’s working!”

Liu Cheng stood up excitedly, and after a quick thought flashed through his mind, he immediately ordered the preparation of another solution.

The process was repeated a few times.

The bottom right, bottom left, top right, and top left corners of the door…

After they completed experiments on all four corners of the door, Liu Cheng returned to the door confidently with the fifth solution in his hands.

He no longer continued experimenting on the corners of the food and instead boldly poured it on the center of the door, leaning to the left!

Hiss!

Hiss!

The moment the solution and black material made contact, it evaporated into a significant amount of white gas, and a pleasant fragrance began to spread.

The black surface of the door began to fade rapidly and gradually transformed into a faint silvery color.

However, the color also did not last for long and gradually settled into a white color that was incompatible with the surrounding of the door.

“It’s a success!”

Before the high temperature spread out of the door’s surface subsided, Liu Cheng excitedly picked up a scraper and lightly tapped on the newly exposed white surface.

The white layers began to be scrapped off like mud.

Finally, something new gradually began to emerge from beneath it…

A keyhole!

“We uncovered the door’s lock!”

They used the detector to determine the general structure of the door’s interior design and locate the “lock cylinder.”

Afterward, they eroded the protection layer above the lock cylinder with the solutions and uncovered the keyhole to “insert” a key.

Liu Cheng’s plan was exceptionally successful!

At the same time, he subconsciously discovered new information about the building after seeing the design of the lock.

“Captain, this door…no, this building. I’m ninety-nine percent sure that the creators were humans.

“We’re extremely familiar with the structural design of this lock and have even participated in a similar project in the past!”