"Huh? What's that sound?" The dark passage was long, and it was unknown where it led to. Chen Zhen suddenly pricked up his ears to carefully identify something as he quietly walked in the passage. However, the sound insulation effect of the castle walls was very good. Although the distance from the entrance behind him was less than 2 meters, the outside sound transmitted here was almost non-existent. If it weren't for the terrifyingly serene atmosphere here, Chen Zhen wouldn't have heard anything at all.