Soon, the party was near the pointed object. They saw that they were strangely-shaped transparent blue icicles, some with a light drizzle of snow on them, while some still dripping. This looked like a hole.

"It's an ice cave." Sierra told the others, "We've been here a few times and we're familiar with it. It's really beautiful inside. Let's get in quickly."

The others didn't hesitate to follow Sierra. William pulled out his laser gun and ran to the front of the line. He had to keep the others safe -- he was worried about the danger.

Near the opening there was still a little light able to let in, but after getting deep inside, all was darkness. The wind blew in and out of the cave, not quite as strong as it had been when they were climbing, but it was still easy to turn the simple wind turbine. So William was in the front, Sierra and Ranran behind him. Ranran also held a laser gun, while Sierra held the generator to light the path ahead.

"We're losing height, boys," Peter told them all, "and we'll soon be somewhere more open -- oh, look! There it is!"

The diode in Sierra's hand shone forward. Amid the exclamations of the party, a great hall appeared in front of them. Looking around, they could see icicles of varying lengths on the ceiling, patterns of ice on the walls, as well as indistinguishable signs. At their feet, twelve identical circles of ice were regularly arranged in a circle around an icicle in the middle of the hall.

The curious party approached the patterns and strange signs. Using the light from the diode, they could see that the outline of Maxwell Snow Mountain was drawn. On the side of the mountain, there were some tiny dots, and those were the planes that were racing in the endurance championship. "It must be you at the head, Rebecca." Sierra said.

"Maybe, ha ha ha." She smiled, "I hope so."

"Oh, look, we're curious to know what these signs stand for." Photon said to Natalie. The others walked up to them.

Just now they couldn't recognize it because they were so far away. The symbols were actually shapes and numbers:

"Eek, what is the meaning of this?" Asked Ranran, "Are we supposed to find the law?"

"Yes. If you answer correctly, you will get something from the icicle." Said Peter mysteriously.

William thought hard. "Three and three... There's a one again. And two?" He seemed to have found the answer, but he told himself he couldn't just trust his hypothesis like this. "Let me test it," He said to himself.

The two remaining triangles fit his hypothesis perfectly. "I know!" He shouted excitedly, "For each triangle, just take the number on the top as the base and the number on the bottom left as the exponent. Then raise the power and multiply it by the number on the bottom right! So the answer should be..."

Before he could finish, Natalie pressed "1822500" on the buttons next to her. The twelve round blocks of ice whirled, and a moment later a crack opened in the icicle and out slipped a green key. "Keep this." Photon reminded his master, "We may need it." William quickly put it into the backpack, and after admiring the beautiful patterns of ice for a while, he and the others moved on.

The wind died down, and William was finally able to concentrate on the beauty of the cave without the biting effects. The ice above Photon now sharpened like the fangs of beasts. There were similarly shaped blocks of ice along the road below. Some of the ice was round on top of the cave, like the eyes of beasts. From afar, it seemed as if there was a real beast guarding the cave.

A drop of water fell on Ranran's black hair. She wiped it off and placed her hand under that icicle, and soon another drop of water fell into her palm. She looked through the drop of water and found a clear reflection of her own in the water, so she had an excited smile on her face.

"Oh, dear, another discovery!" William found a red key.

What they didn't expect was that there was a checkpoint in the cave. The computer map had pointed out that there was a checkpoint nearby, but did not specify its location.

Checkpoint 26 is cleared. Energy charge: 3%.

"Great, the energy core is more than half full." Thought William.

"You used to come here a lot?" Ranran asked Sierra. "Not often, just occasionally." She answered, "But Peter and I are happy every time we come."

"So was it you who solved that math problem?"

"We actually designed it, so surely we know the answer."

Diode lighting up, the scene was more and more striking. The scene had been a beast, and now it was a giant. He looked dreamy in the crystal blue all over. There was a letter "G" on the top of his head, and he looked straight ahead with his bright eyes. He straightened his chest and raised his arms in a "V" shape.

Ranran stared at the giant ice sculpture. "You made this, too?" She asked. Sierra nodded.

Peter told her that it had taken them two months to build him.

"That's nice." Ranran said with a hearty sigh, "I almost thought it was real."

"Wait a minute, don't leave yet." Natalie called to William, who was at the front of the line with his laser gun, "Here's a blue key."

Peter hurried over, saw the key, and said, "OK, we'll be out soon. But first you can take out the other two keys, and then we'll go and see a mysterious object."

"Oh? What can it be?" William asked curiously, but Peter just smiled mysteriously.

After turning several corners, the road made of ice formed a fork in the road. "We'll take the branch on the left, and when we finish using the keys, we'll come back here. The branch on the right will tell us how to get out." Sierra said.

The others followed her instructions and successfully found the mysterious object Peter had talked about. They were two sliding doors, each of which was a giant block of ice. There were three keyholes in the middle of the doors. The left side was marked with red, blue and green respectively, while the right side were three eight-digit turntables, yet there were only two options: 0 and 1. Below the keyholes was a monitor.

"Press," Said Peter, walking to the door and clicking on the monitor. And then it randomly showed a color. Sierra pulled out the notebook she found on the hillside, found the words "color contrast table" in the catalog, and turned to its page. The others gathered to watch.

"I found it! This color has an RGB value of 163,89,217." Natalie saw a legend with exactly the same color as the one on the monitor.

Photon went to adjust the number.

Red: 1010 0111

Green: 0101 1001

Blue: 1101 1001

After adjusting, he inserted all the keys and twisted them. The door opened.

Behind the door was a tall monument carved with ice. It was in the shape of an airplane with the words "Robertson 100-hour round-the-planet flying endurance championship" written on an engine made of ice. It also used a counter rotating propeller and had four blades, each with a trophy painted on it. The wings were covered with the names of champion pilots and planes, arranged in ascending order of year. The left side of the fuselage was inscribed,

Hats off to the champions!

And on the right side of the fuselage was inscribed,

Come on, new players!

The corridor echoed with gasps. "Unbelievable!" William said, "You must have spent longer making this ice plane than the giant."

"You're right, but this guy can fly," Sierra laughed.

"What? Wow, this great?" Ranran cried in surprise.

"Yes." Sierra replied, "We're not using a turboprop engine -- that heat would melt this structure of ice. We used an electric motor, which works well, but we are still a long way from a real racing plane."

"That's already pretty good." William complimented.

"By the way, you know that I come from the same family as the old man and Woodford, but has either of them mentioned to you about a plane called Connor?"

"Oh? Yes. Your father told me. Once Rebecca was recalling aerial refueling, and thanks to his help, she was able to recall the essentials perfectly."

"Well, that's good. We two are going to call him over and do a little air show with this plane. The top of the mountain is wide, but it's not big enough for Connor to take off and land, so we're going down now. I'll email him and he'll be here soon."

"It's wonderful!" Everyone cheered together. "But is there a runway available for this monument plane?" Photon asked.

"You bet. Look, this is the way to the runway." Pointing to a wide road behind the monument, Peter said, "We can go down on an ice slide. Come with me."

They returned to the fork in the road and turned right. After turning a few corners and descending some steps, a huge circular passage came into view. "This slide is long, but it won't make you go very fast. So you'll have plenty of time to look at the ice sculptures around you." Sierra said.

As she spoke, William walked to the start of the slide. He did see that both sides were covered with delicate patterns. There were violets and lavender, two bright mother stars, lofty Maxwell Snow Mountain, streams, forests and small bridges, as well as Hans the engineer's windmills... This, he thought, was almost all the landscape on the planet. He would soon discover that there was plenty of other scenery ahead of him, but because of the limited number, the patterns would repeat themselves over and over again when they had seen them all, but that did not make them any less beautiful.

"Let's get started." William said. The party quickly lined up and slid down. Natalie and Rebecca wished they could go more slowly because their eyes were already too busy admiring the ice sculptures. Ranran stuck her finger on a pattern of a snow mountain. A drop of water stuck on her hand, reflecting the crystal blue light and her smile. William, for the time being, was left with the word "unbelievable".

It was getting darker and darker ahead, for they were coming down and it was not yet daylight. At last William saw again that the mountain stream was rushing into a larger river. He knew that the exit would soon be reached.