I'll tell people who have read the novel that this cave is Marshal's magic workshop, which contains all kinds of human works of art by Ryunosuke and Caster, human intestines and other internal organs, and too many Dongsi that want to be inlaid. So when Caster returned to the workshop after seeing Cybertron for the first time, because Cybertron denied that he was Joan of Arc, he caught the girl who was caught in the workshop because he wanted to vent (the girl's hands were tied and hung on the wall, and her intestines were taken out by Ryunosuke). When the musical instrument hits her intestines, it is connected to the girl, because Custer uses magic to keep her alive, and the camera is fixed on it, so we can't see anything. Later, the emperor set a torch and the whole place burned down. There must be these things in Lao Xu's works.