A long time ago, Buddhist monks carved Buddha's statues in every space possible ! Giant Buddhas, tiny Buddhas unfinished Buddhas, some regular sized Buddhas, painted Buddhas and sometimes, nothing O_O.
Really, sometimes you enter a cave, the place is huge, the lighting is mysterious and even the smell tells a story. They dug into it to create raw columns and, nothing. Did they moved the statues to preserve them ? I don’t think so because the walls seemed clean. Did they used the space to meditate ? I don’t know, I couldn’t read the Chinese sign. But after reading a bit about Buddhism it could make sense. It is a lot about peaceful emptiness.