Like Earth, the Moon had a layered internal structure. From its center to its surface, it could be divided into three layers: the Lunar Core, the mantle, and the crust.
The crust and mantle together were roughly 1,000 kilometers thick, and Nie Yun was currently at the boundary between the mantle and the Lunar Core!
These black stone pillars had effectively forced the Moon's Lunar Core and mantle apart, creating this underground world.
Nie Yun guessed that, perhaps when the Moon first formed, a unique cosmic environment capable of producing energy crystals had existed here. Some interstellar civilization had subsequently discovered the place and mined every last energy crystal through a massive extraction operation.
What remained was nothing but mining waste...
The thought left Nie Yun feeling rather cheated. It was like having a pile of dog crap right outside your front door, only for some passing stranger to step in it before you even left the house!
If not for that damned passerby, he would have been the lucky one!
My energy crystals! It hurts so much...
Wait! Something still doesn't add up. With a mining operation this huge, why hasn't anyone shown up after all the time I've spent bouncing around over their heads?
When I was planting mushroom clouds, it was practically like banging gongs, beating drums, and setting off firecrackers on their doorstep every day. Are aliens really that tolerant?
Were they born Nian beasts, scared out of their wits?
And looking at these traces... they seem really old. It doesn't look as though anyone's been active here recently. Could they have mined everything out and already left?
Finding nothing else unusual nearby, Nie Yun decided to follow the now-faint tracks on the ground and see whether they would lead him to the aliens' mining base.