This passage was an abandoned mine cave, surrounded by solid rock. As Yan Fei stepped inside, he found it damp yet not oppressive, as there was still air slowly circulating. It indicated that although the mine had been isolated from the outside world for many years, other passages must have connected it to the surface, otherwise there wouldn't be so many rats here.
Guided by the 3D map in his mind, Yan Fei continued on his way. Ahead of him was a downward slope, and as he moved forward, he shooed away the rats in his path. Gradually, he noticed water droplets beginning to seep from the stone walls ahead, becoming more numerous the further down he went. Eventually, the walls began to exude a continuous trickle of water which pooled into a stream on the ground, flowing towards the lower parts of the mine.