The Last Trial is Easy?
«Guryuu-en Great Volcano» probably has fifty floors.
Since it was the current floor Hajime's party was in. The "probably" part was because the floor's situation was a little special. Frankly, they didn't understand anything about the current floor.
But more accurately, Hajime's party were currently on board a brown colored boulder, like a small boat, on the magma that was flowing like a big river, mid-air.
"It feels like Indiana-san in hard mode eh..." Hajime muttered while recalling the Earth's most famous and too aggressive Archeologist.
As for the reason why they were in this situation... truthfully, it was Hajime's mistake. Hajime's party had noticed the magma that continued to scorch them, was sometimes making unnatural movement while they were searching for the Serene stone right before they completed the floor.
More accurately, the flow of the magma greatly changed even though there was nothing obstructing it before, or the current suddenly slowed, or there was only a part of magma flowing in the air, and it overflowed, thus the magma dripped below.
However, those happened on the magma away from the passage, so they didn't worry about it because it would not disturb them from conquering the floor. However, Hajime by chance used "Mineral Enquiry" to the surrounding and found out that the cause of the magma's unnatural movement was "Serene Stone." It seemed the magic power inside the magma was calmed by "Serene Stone," similar to obstructing the magma flow.
Hajime's party then thought that the place where the magma's movement was strongly obstructed would have a large amount of "Serene Stone." Thus they searched for it and they indeed discovered a large amount of "Serene Stone" buried in that place. While noting the magma's movement, Hajime's party collected a considerable amount of "Serene Stone." Afterwards, they came to a certain location while thinking there would be much stone in reserve.
It was a place enclosed by the magma flowing in mid-air like a huge wall. Hajime transmuted a stair to approach it and came to know that a large amount of "Serene Stone" was buried there when he used "Mineral Enquiry."
Immediately, Hajime used "Mineral Separation" to only collect "Serene Stone," but he was careless because he kept collecting "Serene Stone" due to lack of concentration from the heat. He didn't put much attention to the surrounding wall of magma.
Hajime noticed this mistake when he stored the "Serene stone" into "Treasure Box." It was because magma spouted with tremendous momentum from the wall the moment the effect of "Serene Stone" had disappeared.
Hajime immediately jumped back, but the magma was spouting with tremendous power just like water gushing out from the cracked and thus collapsed dam. The hole from where it spouted expanded and more rushed out.
The overly tremendous momentum of the magma made the surrounding immediately filled with magma. Hajime used transmutation to create a small boat before Yue's barrier was broken, and the party boarded it. The small boat was immediately heated up by the magma, but there was no problem since Hajime had strengthened the boat using "Strength Endowment" derived from "Vajra."
Following that, they continued to drift along the flow of the magma and was flowing mid-air before they were aware of it. They flowed into the depth of «Guryuu-en Great Volcano» using different route from the stairs. Flowing as they felt the scorching heat from the streaming magma, and ended up where they were currently at.
By the way, normally they would've stopped on the riverbed when they were about to ride on the magma's sky road, but Shia used "Effect Endowment" of gravity magic to reduce the boat's weight, and thus they were able to get on the magma. "Effect Endowment" made it possible to adjust the weight of the thing Shia touched as if it were her own.
"Ah, Hajime-san. There's another tunnel."
"We art almost at the level of the foot of this mountain. Be prepared, okay?"
Seeing the direction Shia pointed at, Hajime's party was would indeed continue to flow into a big hole on the wall along with the magma. They understood the magma was continuing to flow downward. Until now, they've entered a tunnel every time they descent a floor, it might be a shortcut if compared to normally using the stair.
While nodding at Tio's advice, Hajime's party drifted into the tunnel. The magma's sky road was continuing in the middle of the big tunnel like a snake. After the magma's sky road was going lower, it suddenly cut off right after a curve. No, more accurately, it was a sudden downward slope similar to a waterfall.