Zang Feng wanted to understand this section, and even raised his head and carefully examined the top wall of this secret room. Zang Feng saw that around the top wall, there were indeed countless aquatic plants, floating and swinging in the water. In addition, there are countless small fish swimming out of the aquatic plants on one side, swimming around for a while on the top wall of this secret room, and then burrowing into the aquatic plants on the other side. Apparently, this is clearly the bottom of a lake. It's just that, without the hint of frost, Zang Feng couldn't have imagined that this was the mirror lake next to the cabin where Frost lived in the 'Medicine Immortal Valley'.

So, Bingshuang couldn't help but sigh: "I really didn't expect that the secret room of our Medicine Immortal Valley would be at the bottom of the Mirror Lake in our Medicine Immortal Valley, such an obvious place!"

Frost said: "Haven't you heard: the most dangerous place, that is, the safest place?"

Zang Feng said: "Yes! If it weren't for the Frost Girl telling you, the disciple wouldn't have imagined that there are still so many hidden mechanisms at the bottom of our Mirror Lake! If we had known it a long time ago, we might as well come directly to the shore of Mirror Lake and jump into the water, wouldn't we be able to enter this secret room?"

Bingshuang laughed and said, "What you think is beautiful! Look at it, above this top wall, there is a lake nearly 100 meters deep, where did you come from to enter this secret room? If there is really an entrance above, won't all the fish at the bottom of the lake come in? That is, there is a little bit of a tiny gap, and the lake water above will all pour in!"

Zang Feng heard this and exclaimed: "Ah! So in this case, the underground water system that turned left and right before is the only entrance and exit leading to this secret room? Hey, this secret room seems to be very obvious, but if you want to enter, it is also winding!"

Frost listened and said, "Let's not talk about it, the underground water system is not the only way to enter and exit the secret room." In short, if you want to enter this secret room by jumping into the water of Jinghu Lake, you can't do it anyway! Even if there is a master diver who dives to the bottom of Jinghu Lake, let alone being able to enter the secret room, even if you want to find a little clue about this secret room, it will not work!"

When Zang Feng heard this, he asked in surprise: "Ah? Could it be that even if someone sneaks into the bottom of the Mirror Lake, stands on top of this transparent top wall, and passes through the top wall, they can't find that there is still a hole in the bottom of this Mirror Lake?"

Frost smiled: "Of course you can't find it! Even if someone dives under the water and stands on the top wall of this secret room, they will only think that they are standing on a smooth pebble rock at the bottom of the lake!

Zang Feng heard this, and exclaimed: "Ah! Our transparent top wall, from the outside, looks inside the secret room, it is even opaque! Then what is the top wall of our secret room?"

Bing Shuang said: "Actually, the top wall of our secret room is not an unusual object, just a huge natural crystal that is transparent on one side! Moreover, our secret chamber is just above the focal length of this convex lens. Therefore, even at night, the crystal convex lens on the top wall of the secret room can gather the light of the stars in the sky above the lake surface into the secret room. In the secret room, it will also look extraordinarily bright!"

Zang Feng heard this, and couldn't help but say: "No wonder, the light in this secret room before has reflected the roots of those old trees outside the secret room blue! It turns out that it absorbs and gathers the cold flame light spit out by our snowy divine birds in the sky!"

Bing Shuang said: "That's right! Moreover, it's just because our secret room is above the focal length of the single-sided transparent convex lens on the top wall. When we look out through the top wall in the secret room, whether it is the plants in the water or the stars in the sky, they are as clear as if they have been magnified by a telescope! Otherwise, how could you have recognized at once that the birds in the sky were our snowy birds!"

When Zang Feng heard this, he said in amazement: "Ah! The top wall of this secret room is not only a telescope, it is simply a single-sided transparent astronomical telescope!"

'Frost' laughed, "You're getting more and more exaggerated!"

Hiding it but said: "Where is this an exaggeration! To say that our top wall crystal is transparent on one side, and the light in the secret room cannot penetrate to the outside, it is really wonderful! No wonder the disciple was tied to the shore of the Mirror Lake by the Frost Girl at the beginning, even at night, he never found that there was any light coming out of the bottom of the Mirror Lake! Moreover, because the top wall is transparent on one side, the magic weapon of our sect hidden in the secret room at the bottom of the lake naturally cannot be discovered by outsiders!"

Frost said: "You have finally discovered the key to the secret room outside! I have been assigned by the master of the sect, and I have secretly transferred the key treasures of my sect to this secret room. Even, including the Flying Knife Warrior, the foreign "Medicine Immortal Sutra" that he had always wanted to take away, was hidden in the stone wall bookshelf of the secret room at the bottom of the lake at this moment! Moreover, Ling Xu's master, let me secretly transfer these key treasures sent by me to this secret room at the bottom of the lake, also for another layer of defense! Now, take a closer look at the transparent top wall, I don't know, this heavy defense, can you see it?" After saying that, he began to look at Zang Feng, waiting for an answer.

When Zang Feng heard Bingshuang's question, he raised his head again, and looked at the top wall of the secret room again, carefully examining it. However, through the single-sided transparent crystal convex lens on the top wall, Zang Feng suddenly saw a seven-colored figure, "whooshing" on the surface of the mirror lake above his head, floating quickly, as if he was looking for something. At this time, it was really Zangfeng, and he was immediately scared into a cold sweat. But Zang Feng suddenly remembered: when he and Bingshuang were in the snow-capped mountain area, the two of them hid under the ice, and the seven-colored shadow man, even if he floated over the ice overhead, didn't even notice the two of them at all!

So, Zang Feng couldn't help but exclaim: "Ahh However, he really didn't find out that there are still so many secrets hidden at the bottom of this lake!"

Hearing this, Frost immediately praised Zang Feng: "That's exactly why! We hid the treasure under the water, and it was precisely because of the bottom of the water that it was the blind spot of the Demon Sect's envoy Seven Colored Shadow Man!"