Gray Source Castle was located in the inner ring of Ice Saw Valley's second level. It was the core of the entire Ice Saw Valley fortress and the personal residence of the God Lich Sanger.
Although, viewed from above in three dimensions, Ice Saw Valley was a split, hollow gorge within the Underground World, the Ice Saw Valley fortress was actually a complex built upon a solid crater at the center of a Blue Crystal belt.
From the inside out, the Ice Saw Valley fortress was divided into five levels.
The first level was Ice Saw Valley's forbidden zone, as well as the crater's highest region.
It was said that the most important secrets of the Ice Saw Valley fortress were hidden there, and no one was permitted to approach carelessly.
The boundary between the first and second levels was guarded by Sanger's bone dragon legion and even more powerful sentries, more than enough to prove the importance of the place.
Even during the many wars throughout history, this forbidden zone had never been disturbed by outsiders.
The sole exception had been Luo Linna's recent operation.
She had successfully used the opportunity created by the black dragons and demons' United Legion battling Ice Saw Valley to secretly destroy the Seal of Divergence Sanger had sealed there.
The second level was Gray Source Castle.
This castle had stood in Ice Saw Valley for tens of millions of years. Its most recent renovation had been more than eight hundred years ago.
There were not many people in Gray Source Castle. Those who could establish themselves here were all trusted confidants of the God Lich.
Much like the first level, this was not somewhere ordinary residents could approach.
Beyond Gray Source Castle lay Ice Saw Valley's third level.
This was considered the main