The Netern Crystals are magic crystals considered ancient artifacts on the same level as the legendary sword of the Drenn family, as they emerged in the same era. Attempting to emulate the nature of the Eclipse Amulet, the crystals when gathered connect a certain coordinate to its counterpart on the opposite side of Netern, creating an interdimensional portal, capable of taking a living being to the opposite side or pulling back someone who has already entered the portal.
Once used, the crystals disappear along with the portal, and then return to their respective altars, located in the four dungeons of the Valley of Music. Each dungeon is located inside one of the mountains of the valley, and their entrance gates are extremely resistant, requiring an extraordinary level of strength or the skills of an experienced swordsman.
The Mount Sorang dungeon has a traditional dungeon structure, with mazes and traps, but they are randomized through an electronic system, powered by the mountain's power grid. This system, however, was implemented a few decades ago, when the technological revolution reached Netern Island. The power grid itself that surrounds the dungeon gate counts as one of the challenges.
The Haidora Peak dungeon is mostly made up of ice and snow, adding a greater difficulty to its challenges, with slippery floors and hidden snow traps being prime examples. The trail to the entrance gate is arduous, as a constant blizzard falls on the trail, and snowballs frequently roll down the mountain, trampling anyone who dares to walk through the trail.
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The Kageki Caves dungeon is a large, dark maze that connects several of the mountain's caves, making it easy for those with poor sense of direction to get lost. There is no challenge at all before entering, but staying on the right path is the hardest part of the exploration.
The Great Noogard Hill dungeon was created with the intention of being the last and hardest of the four dungeons, the final test for those who wish to collect the Netern Crystals. The starting room connects to five corridors, two on each side and one in the center. Each corridor leads to a different door. The side corridors lead to the dungeon's inner challenges, each representing one of the previous dungeons: Light, Ice, Shadow, and Wind. The Wind Challenge, unlike the others, consists of a mixed path combining elements from all the other challenges. Each inner challenge leads to a button. When all four buttons are pressed, the gate in the central corridor finally opens, leading directly to the crystal's altar.
Few people have dared to venture into these dungeons for decades, primarily due to the belief that the other side of Netern is a merciless and cruel place, and the second reason being the fact that the Netern Crystals had disappeared since the most recent war between the Etykiran families.