Shen Fei took a step forward, and Xiao Ning'er followed at his side.
They passed through the two ink-dark lines suspended in midair. The lines trembled slightly as they passed, as though confirming something, then dissolved into fine wisps of mist that drifted back into the depths of the cave entrance.
The passage inside extended much farther than it appeared to from outside. The rock walls on either side were rough and uneven, with occasional, exceedingly faint carvings. Their patterns shared the same style as the blurred lines on the outer wall: simple and ancient, with no discernible meaning.
The passage was dim, but not so dark that they could not see their hands before their faces. Tiny pieces of luminous ore were embedded deep in the rock walls. The grains were small and unevenly scattered, with only one every few paces, barely illuminating the path beneath their feet.
The floor was natural stone, with little sign of human polishing. It rose and dipped underfoot, and loose stones occasionally rolled beneath their soles.
The farther they went, the drier the air became. The temperature was actually somewhat warmer than outside, carrying an indescribably deep, weighty presence, as though something had slumbered in this space for so long that even the air had become steeped in it.
Shen Fei led the way, extending the Shadow Mantis's perception to cover a range of several dozen yards ahead and behind.
He could feel the passage descending. The slope was so gentle it was almost imperceptible, yet each step landed half an inch lower than the last.
The passage rounded two bends, neither particularly sharp. Walking through them felt unremarkable, but Shen Fei kept track of their direction in his mind and knew they were heading roughly east-southeast.
Xiao Ning'er followed half a step