Su Yao and Ling Yu carefully studied the ancient characters and patterns on the basement walls. The information was obscure and difficult to understand, but they did not slacken their efforts. Su Yao's system continuously analyzed and deciphered the text, gradually piecing together some clues.

According to the clues on the wall, the energy key appears to be divided into several parts, scattered throughout different areas of the castle. The key to solving the puzzle lies in activating the runestones hidden around the basement in a specific order.

They began by searching for fragments of the energy key. Su Yao used her spatial abilities to explore every corner of the castle and quickly found the first fragment in an abandoned study. This fragment emitted a soft glow and was engraved with unique patterns that echoed some of the designs on the device.

While searching for the next fragment, they reached the top of the castle tower. A fierce wind howled at the top, and the surrounding area was littered with ice, snow, and broken debris. While clearing away the debris, Ling Yu accidentally triggered a mechanism, and a volley of ice arrows shot towards them from all directions.

Ling Yu swiftly used his ice-based abilities to erect a thick ice wall around them. Ice arrows struck the ice wall, producing a crisp impact. Taking advantage of this opening, Su Yao used her spatial abilities to locate the source of the mechanism. She discovered a small box hidden in a corner, surrounded by trigger devices.

Su Yao carefully used her spatial abilities to move away the surrounding triggering devices, opened the box, and inside was the second fragment of the energy key. However, the moment she obtained the fragment, the castle began to shake violently, seemingly triggering a more powerful defense mechanism.

They hurriedly returned to the basement, only to find it now filled with ice spike traps. Su Yao used spatial teleportation to skillfully avoid the ice spikes with Ling Yu, continuing their search for the order to activate the rune stones.

After some effort, they found some subtle clues about the order of the rune stones. Following these clues, Su Yao and Ling Yu began activating the rune stones one by one. Each time a rune stone was activated, the light around the device would intensify, but it would also trigger new dangers.

As they activated the penultimate runestone, a large amount of black smoke billowed from the basement. This smoke was corrosive, causing objects to sizzle and crackle wherever it went. Su Yao and Ling Yu covered their mouths and noses with their clothes, but the smoke continued to erode their bodies.

Ling Yu used his ice-based abilities to create ice blocks in an attempt to disperse the smoke, but the smoke quickly melted the ice. Su Yao activated her spatial abilities, creating a temporary isolation space around them, buying them some time. Inside this space, they discovered that the smoke was emanating from a drainpipe in the basement.

Su Yao used her spatial abilities to seal the drainage pipes, gradually slowing the rate at which the smoke billowed out. They quickly activated the last rune stone, at which point several slots appeared on the device specifically for holding fragments of the energy key.

They placed the found fragments of the energy key into the slot, and the device began to emit a bright light and a booming sound. Within the light, a virtual image appeared, displaying a map marked with specific locations that seemed closely related to the source of the apocalyptic extreme cold.

At the same time, the device released a large amount of supplies, including various advanced technological equipment, warm clothing, and precious energy. Su Yao excitedly used her spatial storage to store these supplies, which would greatly enhance their ability to survive in the apocalypse.

But they knew this was just the beginning. According to the map displayed in the images, they needed to travel to the marked locations to further explore the secrets of the post-apocalyptic extreme cold and find a way to completely change the world. After a brief rest, Su Yao and Ling Yu, carrying new supplies and a mission, left the ancient castle and headed towards their unknown destination. Their figures faded into the distance amidst the post-apocalyptic snow and ice, becoming sparks of hope in this icy wasteland.