The entrance to the underground library is just in the southeast corner of the proving ground.

It was a bottomless tunnel, and the builders of the test site had embedded a rather thick iron door in the entrance of the tunnel, and now the iron door had been broken open by the thief, and when I looked through the doorway, I could only see the darkness that could not be penetrated by the light, and the black fog that swirled and floated in the tunnel.

The Thief said that the tunnel was quite dangerous, and that the shadow guards should not approach it easily.

At this time, the shadow guards were just standing silently thirty or forty meters away from the tunnel, and only Tai Sui was sitting in front of the iron door that had been stolen.

Before, Tai Sui obviously asked the thief saint to prepare the materials as soon as possible, and the thief saint also agreed, but five or six hours have passed, and the thief has not returned.

This made Tai Sui very upset.

If it weren't for the thief's instructions before leaving, Tai Sui would have waited for him to come back, and he would never enter the tunnel alone, Tai Sui would have gone down a long time ago.

Recalling the extremely serious expression when the thief was leaving, Tai Sui felt an inexplicable awkwardness in his heart.

That expression was as if the thief could conclude that Tai Sui would not be able to face the danger in the depths of the tunnel alone.

Tai Sui really hates when people question him.

But he also knows that when the thief saint is serious, what he says is worth listening to, this guy is rarely serious, but once he is serious, he will become quite wise.

Well, this thing is a fool when you're not serious.

Nine hours had passed, and the Thief had finally returned, bringing with him two large backpacks, four lamps, two rather long chains, and a hook on the head of the chains, and a large roll of rope on his shoulders, and a birdcage in his hand.

The four valve lights have been specially treated with moisture protection, the chain claws also look freshly forged, and the bird in the cage, needless to say, must have been caught.

It's no wonder that the thief has been gone for so long, and it takes a lot of time just to get these things.

The thief rushed to the mouth of the tunnel like a gust of wind, then tied the birdcage with a rope and drove it into the tunnel.

Tai Sui was curious, so he asked the thief saint, "What are you doing?" ”

"Check the air quality first, don't look like you're strong, if there's no oxygen underground, you won't stay in it for long. Originally, I wanted to find two oxygen tanks, but unfortunately, there were no such things in the park. ”

The Thief said as he continued to release the rope, causing the birdcage to slide down the tunnel.

There are no ladders in the tunnel, the ground is an inclined plane with a considerable slope, at first, every time the thief releases his hand, the rope only stretches out a dozen centimeters, but later, the friction in the tunnel seems to have disappeared suddenly, every time the thief lets go, the rope slides towards the tunnel, and a slip is several meters.

Until the entire rope was almost completely submerged in the tunnel, the thief held the end of the rope with one hand and probed into the tunnel with the other, testing the slope of the tunnel.

After a moment, the thief breathed a sigh of relief and said to Tai Sui: "If the slope of the tunnel has not changed, the vertical descent depth of the birdcage should be more than thirty meters. ”

Tai Sui nodded: "In such a deep place, the air quality should be quite poor, and the birds in the cage are estimated to not live for a few minutes." ”

The thief pouted and didn't say anything.

Ten minutes later, the thief pulled the bird cage up, and frowned when he saw that the bird in the cage was still alive.

Tai Sui also realized that something might not be right in the depths of the tunnel.

First of all, he didn't expect the tunnel to be so deep, and secondly, the air quality in the depths of such a narrow tunnel should be very poor in common sense, and even if the birds that were put into it did not suffocate, they should not have any suffocation reaction at all.

The thief saint spoke: "I am afraid that there is a rather large oxygen containing pool in the depths of the earth. ”

The so-called oxygen tank may be a large-scale underground palace, with complex underground water veins, or it may be a large underground karst cave that has not been explored by humans.

Of course, Tai Sui knew that there must be an oxygen tank deep underground, but he couldn't figure out why the thief saint specifically mentioned this matter: "What does this mean?" ”

The Thief took a deep breath: "At present, I can be sure that this tunnel is connected to the legendary underground library, a large underground palace building like this usually needs to be insulated after it is completed, otherwise the building structure inside is easily oxidized and corroded. But at present, the oxygen in this underground palace is extremely abundant, and the reason why this is the case may be because the people who built this underground palace have kept a large number of living creatures in captivity in the underground palace, and oxygen is prepared for these living creatures. ”

"What living thing?"

"It's hard to say, but I guess that nine times out of ten it is a fierce bird and beast, raised to guard the underground palace."

Hearing the thief saint say this, Tai Sui was a little more relaxed.

In his opinion, as long as it is a living creature, there is nothing to be afraid of, because anything that has a physical body can be destroyed.

The thief saint seemed to be able to see through Tai Sui's thoughts, and took the initiative to remind: "But any species that can survive in the depths of the earth for tens of millions of years is not easy to mess with. I can't say a word or two about how dangerous a dungeon like this is, but I must remind you that you must always be careful when you enter. ”

Tai Sui nodded: "Can you go in now?" ”

The thief handed an iron chain to Tai Sui: "Go down with the chain." ”

Tai Sui was really a little impatient, according to his own meaning, isn't it just a tunnel, just go down, and put some chains, it's really a big deal.

However, Tai Sui still followed the advice of the thief.

He first bolted one end of the chain to a cement pile closest to the mouth of the tunnel, then threw the other end into the tunnel, and when the thief lit the two valve lights, the two of them divided the weight equally, and grabbed the chain and walked into the tunnel.

The normal weight of these two people adds up to nearly a ton, fortunately, they can rely on a breath of true qi to offset most of the gravitational force on weekdays, but even so, if the two of them weigh together, the weight will still be three or four hundred catties.

After the two of them descended a distance of about three meters along the tunnel, most of their weight was on the iron chain, and they heard a sharp sound of "clang", and the iron chain was directly straightened.

The tunnel was so deep that the sound lingered in the darkness for a moment, and only then could a faint echo be heard in the distance.

The thief paused slightly, as if he was thinking about something, and after a short while, he turned back to Tai Sui and said, "Judging from the echo, this tunnel should be more than two hundred meters long, and at the end of the tunnel, it is a giant object made of metal. ”

Tai Sui couldn't help but be shocked, he didn't expect that with just one echo, the thief saint could collect so much information.

"Watch your step."

The thief whispered, then held the valve light and felt deeper into the tunnel.