Fire Element True Qi, an average cultivator might have never even heard of it, but Ling Yunpo of Shushan had.
The reason was nothing else: beneath Shushan, there lay the Fire Element Cave, which also contained Fire Element True Qi.
Those entering needed to shield their bodies with the Xuanguang Ruler, or else, if they came into contact with Fire Element True Qi, they would die, consumed by fierce flames.
This Fire Element Cave had another characteristic, that is, every time Fire Element True Qi erupted, it would melt the nearby cave walls, and after they solidified again, the structure of the cave would be completely altered.
Even if you remembered the way you came, a single eruption would make all your previous efforts in vain, making it impossible to return the way you came.