100 zhang was not deep by Su Yu's standards. After half a joss stick's time, he had successfully dug to the top portion of the secret basement.

A light barrier appeared beneath Su Yu's feet. Through the light barrier, he could clearly see the sealed secret basement. It was not particularly wide, only 30 feet all around. There was only a stone bed and a table within.

There was nothing on the stone bed. But there was a golden imperial jade seal on the stone table. The imperial jade seal was carved with lifelike dragons—powerful and arrogant.

The rest of the items on the table had decomposed, but the imperial jade seal was covered with faint five-colored lightning, thus keeping it fresh and new, untouched by the hand of time.

Su Yu's heart thumped wildly. This was definitely a unique treasure!

Through the barrier, Su Yu could not determine the grade or value of the treasure. But intuition told him that the imperial jade seal might be the most important thing in the entire palace! Concentrating, he also realized that there were nine books on the table. Even though they were covered in dust, they had not decomposed yet.

Anxiously observing the light barrier, he realized that it had a powerful defensive capability, holding back everything from the outside world. If that had not been the case, the 100-zhang layer of earth would have long shattered this secret basement.

Su Yu thought for a moment before taking out the Golden Scale Dagger to see if it would leave a mark on the barrier. But when the sharp end of the dagger came into contact with the barrier, it was as though it was slicing against steel. Sparks could be seen, but the barrier remained unmoved. Then, Su Yu tried with the Nine Yin Yang Formation. But the light barrier barely shook.

Su Yu let out a bitter laugh, realizing he might have been prematurely excited. But that did not mean he was out of ideas.

With a thought, Su Yu sat cross-legged. As he formed seals with both hands, a transparent shadow appeared above his head. It was Su Yu's soul leaving his body. The light barrier could dispel physical attacks, but what about spiritual elements?

Thinking for a moment, Su Yu's soul exerted force beneath his legs. He easily passed through the barrier of light, entering the secret basement without obstruction! Su Yu was elated. It was so easy!

Without hesitation, he immediately made his way before the stone table. He looked at the imperial jade seal. He tried to grab the seal, but in his soul state, his hand merely went past it. He was unable to touch it.

Su Yu sighed. He still had a long way to go if he wanted to reach the level of Yun Yazi, to be able to launch material attacks while he was a disembodied soul. Would he be forced to return empty-handed even though he had successfully made it in?

Annoyed by the injustice of the situation, Su Yu looked at the nine books. They were placed casually on the desk. Even though they were closed, Su Yu could make out their contents by looking through them with his Soul Eyes.

"Hmm… They are all commentaries about lightning-based techniques!

"

Su Yu was a little surprised. He had thought that these were all techniques that had been left behind, but in reality, they were all commentaries—possibly written by the Thunder Emperor himself!

Thinking for a moment, Su Yu concentrated and read the contents. He had not thought too much about these books initially, but the deeper he read into the books, the more excited he became. Of these nine books, the first was a simple summary of lightning-based techniques, the second was an introduction, and the third was the Thunder Emperor's experiences of cultivating his techniques. The fourth, fifth, sixth and seventh books—four full books—were about lightning-based abilities cultivated by the Thunder Emperor! This was akin to his legacy!

The eighth book was an introduction to lightning-based materials. Within it, information about materials for elixirs and artifacts, as well as supporting materials, was abundant. It basically encompassed all the knowledge Jiuzhou had about the subject.

After he finished reading it, Su Yu finally made his way to the last book, which was about the item Su Yu was most excited about: the imperial jade seal!

This imperial jade seal is the prototype created by me, still three stages away from the true Five Element Strong Thunder Seal. It is now only a half-manufactured spiritual artifact. If it were fully forged, its grade might even be above spiritual artifacts! It could become a fairy artifact that would shock Jiuzhou.

A fairy artifact? Su Yu was shocked, what level was a fairy artifact at?

What made Su Yu even more surprised was that the imperial jade seal before him was merely in its beginning stages! For it to work, there were three more steps to accomplish.

Based on Su Yu's understanding, creating an artifact in its beginning stages largely involved combining its materials. Could this half-manufactured spiritual artifact be just an amalgamation of its materials? If merely combining its materials would result in such terrifying power, just how powerful would the completed product be?

Su Yu gasped. Even the high-grade divine artifact, the Eternal Stone King Armor, had not awed him to such an extent. This item was more precious than he could ever have imagined!

Su Yu breathed heavily. He had to have it! But he could not break this barrier. How could he leave here with it?

Boom—

At that moment, a rumble could be heard all over the secret basement. A hallway was faintly visible on the other side of the barrier. It was the door to this secret basement, and someone was breaking in from outside. A crack had already been opened in it.

Su Yu was shocked when he saw who was behind the slit! Gang Dalei!

In an instant, Su Yu understood. Searching for the Thunder Herb was merely one of his reasons for being here. The true goal of the sloppy old man was to find the legacy of the Thunder King.

Su Yu was anxious. If Gang Dalei entered, he would take this prototype treasure!

But suddenly, there was an odd heat in Su Yu's brain.

"Congratulations on reading the nine books and inheriting my legacy!

" said a voice.

Su Yu was shocked. How could the will of the Thunder Emperor still be present in this place?

"This prototype fairy artifact will also be given to you as part of the legacy,

" the voice went on.

"I hope that you can finish my work and continue creating this artifact.

"

After which, there was a creak in his brain as it was filled with a foreign mantra. It was the mantra used to control the Five Elemental Strong Thunder Seal.

Boom, boom—

A rumble could once again be heard from the door of the secret basement. Without hesitation, Su Yu recited the mantra. Immediately, he felt a connection form between himself and the Five Elemental Strong Thunder Seal. Su Yu extended his thoughts, and the surface of the imperial jade seal creaked as it floated in the air.

Su Yu was elated. Under his control, the imperial jade seal quickly made its way to where his physical body was. To his relief, the light barrier did not obstruct the imperial jade seal. The seal passed easily through it and successfully appeared before Su Yu's physical body.

Su Yu was excited as his soul returned into his body. Opening both eyes, he attempted to store the treasure in the Cosmos Mirror without hesitation, but strangely, the object remained unmoved. It seemed as though it was unable to be stored in the Cosmos Mirror.

The mark of the Nine Jade Spiritual Pearl on his arm glowed, and the prototype fairy artifact flashed with lightning as it was absorbed into it. Su Yu's worry eased.

Boom—

A giant thud erupted. The door of the secret basement had finally been opened! Gang Dalei entered holding a crystal-like bat enveloped by lightning with spiritual qualities.