"First, I should think about how to improve the ventilation system of the base, which is one of the most pressing problems for an underground shelter."

As Su Mo sat on the stiff wooden chair that poked his butt slightly, he tried to recall the knowledge he had from the civilization era.

As well as shelter designs from doomsday movies…

Underground shelters required a large air filtration and regulation system, but having any ventilation ducts that connected to the outside was a safety hazard.

That was why Su Mo thought it would be best if he could use an internal air circulation system. However, he would need water and electricity to make it possible for him to electrolyze oxygen for the entire facility's internal air circulation.

Of course, he could not be completely sealed off from the outside world as the stability of said completely sealed environment was extremely poor. That was why ventilation holes to the outside were still necessary.

In order to conceal them, the vents could not be too big and he would also need to have some sort of switch that could shut them close at any time.

If not for the topographic restriction, the optimal solution would have been to design the inlet of the vent somewhere below a rocky area that would only be exposed during low tide in the riverbed, or perhaps on an uninhabited island.

The slender pipes would be able to pump fresh air that had been purified and filtered into the bunker, and the pipes could be closed up during emergencies to be switched to an internal circulation system.

However, with the current conditions and equipment in the shelter, these ideas of his could only remain ideas for now.

After looking around the trading channel for items currently for sale, Su Mo decided to follow the most basic mechanical design.

By using a submarine's periscope structure.

He would carry it out by opening up a window in the center of the shelter that doubled as a ventilation hole and lighting.

The core design was to first dig out a hole in the middle of the shelter's ceiling and to install glass with a good degree of light transmittance.

The next step was to fix some ventilation holes on the glass to ensure that the air could pass through the pipe.

Further along the hole that was dug out, he could carve out a Z-shape inside the hole.

In the Z-shaped hole, he would place two plane mirrors parallel to each other at an angle of 45 degrees. With the light's reflection, daylight could travel into the shelter and solve his problem of illumination during the daytime.

After applying the first layer of ventilated glass, he could next design a layer of mechanical blast-resistant glass that he can shut tight in case of disasters to prevent the inflow of liquid or toxic air.

Even a high school student could come up with such a simple design, but implementing it would be a lot of work.

Without suitable tools, it was a hard task to dig a hole all the way out of the shelter that was five meters underground while maintaining a good degree of accuracy.

However…

"I can count on the system!"

With his current understanding of the system, Su Mo knew very well how to make the best use of it.

When there were no materials, the system required a hefty number of points to magically supply materials out of thin air.

However, when materials were already supplied, the system behaved more like a construction team; only a small number of survival points were needed to finish the upgrade.

After mentally pondering and confirming the feasibility, Su Mo opened up the trading channel.

Currently, he could spend the following resources.

Normal mineral water (1000ml), psychic energy water (600ml), and 10 catties of Dalieba bread.

As for the remaining items—his pet egg and energy bike blueprint—he did not intend to take them out to trade.

Trading channel.

[Seller: Su Mo]

[Trade Item: 50ml Psychic Energy Water]

[Requested Item: blast-resistant glass]

[Remark: It can strengthen the fluids in your body. Don't miss out! I only need two units of glass per customer. It's of good quality. Send me a private chat.]

...

[Seller: Su Mo]

[Trade Item: 15ml mineral water (maximum of 975ml)

[Required Item: 1 iron block (Personal exchange count 1/1)]

[Remark: Each person can only complete one transaction]

After he listed the two items, Su Mo put up another 25ml of water to buy two units of mirrors with good reflection, which exhausted his supply of normal quality mineral water.

Su Mo made a trade offer of 15ml of water for 1 iron block, which was an extremely shady thing for the seller to ask for. However, for some players who were struggling in a matter of life and death, it was nothing less than an offer from a savior.

In addition to that, Su Mo also implemented his idea of how to apply the limit of each person only being able to trade once.

Water was like liquid gold now. He did not mind other people consuming it, but he did not want ill-intentioned people taking and hoarding it.

World Chat Channel.

"People who need water and have iron blocks, quickly go to the trading channel because the Almighty Su is selling water again! One person is limited to only one trade, so hurry up!"

"Holy sh*t! The Almighty Su is in a generous mood today!"

"Hehe. You're too late. Luckily I paid attention to Almighty Su's personal channel in advance so I can get a gulp of water. Haven't you seen his fans? He has more than four hundred thousand fans and you random people think you can grab it?"

"Where does Su Mo get his water? Didn't he just spend 700ml to buy the illustration handbook? And now 1000ml for iron blocks? Does he think he has too much water?"

"Go and check it out quickly. The Almighty Su is selling psychic energy water. It can actually strengthen your body to cure diseases. If you have blast-resistant glass, hurry up and trade him for it!"

"Sigh. Enough with all this comparison. It's pissing me off. I dug all morning and didn't get a single drop of water. Just let me die of thirst already."

"..."

The number of public messages one could send was one per day, but there was still a large group of people gathered in the World Channel to discuss, not to mention the Regional Channel was also in full swing.

Even Su Mo's private messages were flooded at that moment.

It took less than two seconds for his request for iron blocks to be completed and now 65 units of iron blocks sat quietly in his inventory.

At that moment, there were countless people who had other resources but were screaming for a mouthful of water.

"The demand for water is way too high!"

Su Mo privately thought.

In those two days, other people had been listing other resources up for sale in exchange for water whereas he was the only one who was using water in exchange for resources. Naturally, that made him stand out.

Su Mo used the filtering function in his private chat together with the keyword iron block to filter out eighty percent of the useless messages.

After more searching, dozens of private messages mentioning blast-resistant glass were picked out and he started to go through them.

After going through many consecutive private messages that asked for extra water in exchange for normal quality blast-resistant glass, Su Mo finally saw one message that caught his eyes.

Feng Mengyue, "The Almighty Su, I have a piece of normal quality blast-resistant glass, but I think you're probably too good for something that common. So if you're willing to bump up the trade offer, I can trade with you a piece of excellent quality as well as a piece of rare quality blast-resistant glass"

The avatar was a woman with a delicate face and a heroine-like appearance.

When Su Mo read her message of having both an excellent and rare quality glass, his eyebrows jumped and a smile appeared on his face.

So far, the quality standard of items was separated into five levels. Normal, good, excellent, perfect, and rare.

Feng Mengyue seemed to be a powerful woman. She was somehow able to get her hands on a rare quality blast-resistant glass on just the second day. Her impressive luck was evident.

"The first thing she said was to increase the trade offer but she did not take the initiative to say how much she wanted. Seems like she's going to be a difficult person to deal with."

Su Mo shook his head and did not take the bait. Instead, he tried to outsmart her and replied.

Su Mo, "You should understand the value of the psychic energy water. There's plenty of things on the market but what I have is one-of-a-kind since it can enhance the body. As for the blast-resistant glass, I'm buying it to replace my shelter's windows. It actually doesn't matter if it's not as good."

Feng Mengyue, "How about 300ml?"

Su Mo, "Dream on. It's just two pieces of glass. They're not worth that much. If you don't want the water, I'll drink it this afternoon."

Feng Mengyue, "Let me think about it."

When Su Mo saw her reaction, he broke into laughter.

The only person selling psychic energy water in the market was him. He was monopolizing it. If he decided not to sell, no one could do anything.

After two minutes, Feng Mengyue sent him a message again.

Feng Mengyue, "Apart from the two pieces of glass, I'll also throw in some information for 300 ml psychic energy water."

Su Mo, "What information?"

Feng Mengyue, "Information about how I obtained the glass."

After Su Mo read what she wrote on the chat box, he thought for a moment and decided that it was an appropriate deal. 

In the Doomsday world, there was a fixed price on supplies but information was invaluable.

For example, if Su Mo did not have the necessary information to kill the chameleon, even if he wore a full suit of armor, he would have been as good as dead. 

After closing up the private trading channel and uploading 300ml of psychic energy water to the seller, the trade was completed.

[Record]: You have lost 300ml Psychic Energy Water.

[Record]: Congratulations on gaining Blast-resistant Glass (Excellent)*1. Congratulations on gaining Blast-resistant Glass (Rare)*1.

[Record]: Do you want to uncover the information given? 

"Yes."

When Su Mo answered, a person's voice started playing in the empty shelter.

"In the wilderness, ruins are generated at random. When I woke up today, a mysterious ruin regenerated beside my place. It looked dangerous, so I only looted a few pieces of glass at the periphery. When I tried to continue exploring, the ruin suddenly disappeared."