"This is...?" Xu Xin picked up the bottle of gray potion.

[Special tree house root medicine (purple): Pour it under the tree house to promote the development of the roots of the tree house. Each dose of medicine can expand the protection range of the tree house by three kilometers. 】

A purple-grade potion! It’s also a potion that expands the protection range of the tree house!

Xu Xin's tree house's current protection range is three kilometers in radius. After using this potion, it will be expanded to six kilometers in radius! This is not only doubled, the protection radius is doubled, and the area is expanded to four times!

In other words, Xu Xin, who has used this potion for his tree house, can move and explore four times as much as now! And within this expanded range, there may be another resource area.

Good stuff, really good stuff, worthy of being a golden treasure chest.

Xu Xin picked up the thin card again.

[Metal products automatic unlocking contract (purple): can unlock the formulas of all metal products. After using this contract, all metal-related production formulas can be automatically unlocked as long as all types of raw materials are obtained. 】

After the tree house renovation contract, he obtained another contract, a contract related to the metal product formula!

With this contract, Xu Xin can no longer only make stone tools!

[Congratulations, you have opened three types of treasure chests: gold, silver, and copper. You are the first among this group of survivors to find all three types of treasure chests and open them all. The rewards will be distributed after the end of this jungle exploration event. 】

[Survivors please continue their efforts, strengthen themselves, and strive to survive in this world.]

The mysterious voice sounded again.

He is the first to get all the treasure chests.

The event is not over yet, and I don’t know if anyone else will find the gold treasure chest.

To be honest, if Coco hadn't told him there was a gold treasure box down there and insisted on pulling him down, with his cautious character, it would have been impossible for him to get into this hole and dig out the underground passage.

The conditions for obtaining this golden treasure chest are really too harsh.

Xu Xin shook his head, not thinking about it, looked at the contract in his hand and chose to use it.

Just like last time, the card representing the contract was shattered in his hand and integrated into Xu Xin's body. Xu Xin felt a surge of power pouring into all parts of his body.

This time he not only felt stronger, he even felt his mind became clearer. Everything he had just experienced was quickly sorted out in his mind.

First of all, the huge piranha flower should be the monster guarding the entrance to the underground world.

This unexpected iron room underground has been buried underground for many years like the people in it, but the extremely foul-smelling red mist in the room has no idea where it came from.

The person in the room is not from this world, but he came here with tools and food from his original world. This shows that the way he came to this world is different from survivors like Xu Xin, but how did he come here?

Xu Xin can't understand now.

The golden treasure box in this mission is bound to the secret of the underground space. The golden treasure box should have been placed in this position deliberately. The person who discovered the golden treasure box will definitely see this underground world before finding the golden treasure box.

secret.

And those who cannot find the location of the golden treasure chest will naturally not be able to discover the secret.

Who is that mysterious voice? What was the purpose of bringing them to this world? Could it be that when they grow up, they can fight against the monsters deep underground?

How did those monsters come into being? The size difference between them and the creatures on the surface is really huge.

He thought of the giant anaconda in the center of the lake and the giant crocodile at the bottom of the stream. These two unnaturally huge creatures must have come out of the ground, and the connection beneath the lake was probably thousands of meters deep underground.

There is also this potion in the gold treasure chest.

Xu Xin looked at the bottle of gray potion in his hand. The whole bottle was only about 300 ml, and the weight was about the same as a canned drink.

The function of the medicine is to promote the development of the roots of the tree house and expand the protection range of the tree house. Does this mean that the roots of the tree house are what protect survivors like Xu Xin from underground creatures?

A picture appeared in Xu Xin's mind.

During the two hours that the tree house grew, while the tree house on the ground grew, the roots of the tree house also differentiated underground, extending in all directions, up to three kilometers away.

The roots of the tree house are intricately distributed underground, blocking monsters that want to come out of the ground. Once a monster appears, it will be sucked by the roots of the tree house and quickly turn into a dry and brittle specimen.

Therefore, when the roots of the tree house develop longer, the protection range of the tree house becomes correspondingly larger.

Xu Xin thinks this explanation makes sense.

This also explains why the mysterious voice emphasized over and over again that the tree house must not be abandoned, because the tree house is the most powerful weapon and the greatest protection against underground monsters.

After thinking about all this, Xu Xin's mood relaxed slightly. According to what the mysterious voice said before, the monsters underground will not attack them at least in the near future. They only need to concentrate on dealing with the monsters on the ground.

The beast is just fine.

The treehouse will protect them.

Xu Xin put the golden treasure box into his backpack. Although the golden treasure box was made of gold and was very heavy, Xu Xin's strength was no longer the same after being increased several times, and the weight was reduced to 20%.

As a backpack, this treasure chest can be carried on your back without any problems.

He was actually looking forward to what would happen after gathering the three treasure boxes and putting together the pattern.

Before leaving, he decided to take another look at the underground world. After all, after he went out this time, he probably wouldn't come back here for a long time.

Coco did not walk to the edge of the cliff like him, but lay down behind, moving away from the cliff with some fear.

It's still the scene of a bunch of demons dancing around.

Huge monsters covered in seaweed, giant piranha plants that are several times larger than those on the ground, blood-red rattans everywhere, firefly-like creatures as big as small cars, and some other completely different creatures on land.

Impossible giant animals and plants.

These are things he will face in the future.

He must improve himself quickly to give himself the ability to fight against these things!

Xu Xin looked forward, and suddenly his eyes froze.

He saw many downward bulges at the top of the entire underground world.

Xu Xin's position now is equivalent to the lights on the ceiling in the room, and those protrusions are other lights.

"These bumps should be the tree houses of other survivors, or the roots of the tree houses." Xu Xin thought thoughtfully.

According to his inference, the interior of these protrusions should be the intricate roots of the tree house, used to protect the survivors from the intrusion of these underground creatures.

"Although I don't know who brought us here, he must be playing a big game."

Xu Xin took one last look at the underground world, then turned and walked back to the iron room.

The skeleton was still scattered on the ground. Xu Xin grabbed Coco, who wanted to play with the ball, and pressed it on his shoulder.

"Ugh!" Coco yelled with some dissatisfaction, but she still lay on his shoulder obediently.

The next task seems simple but is not simple.

Climb up!

Looking at this deep passage, Xu Xin felt that her legs were shaking.

Just climbing down before made his arms extremely sore, and now he had to climb up again!

He even carries a gold treasure chest!

Tire him to death!

Xu Xin glanced at the little guy on her shoulder: "Can you crawl by yourself?"

"Uh-huh!" Coco shook her head violently.

"You're so lazy!"

"Ugh!" Coco wanted to retort. The distance between each step was almost as long as its body. How could it climb!

Sighing, Xu Xin decided to eat something first before climbing up. After all, he vomited everything he ate last night up there. Although the contract just made his body recover a lot of strength, after staying down there for so long,

I'm afraid it's already dawn up there, and it's time to eat.

Just when he took out an apple and wanted to gnaw it, a hissing sound of deflation suddenly came from beside him.

"what sound?"

Xu Xin turned around warily.

In his horrified gaze, the half-open iron door suddenly closed automatically with a loud noise, and then a familiar red gas spurted out from the gap between the wall and the floor of the iron room, gradually spreading.
Chapter completed!