Is that "stage" surrounding the robot/mecha some kind of rock formation like those formed naturally by erosion? But around it are walls and a floor made of wooden planks? The difference in size and proportions of the stairs and platforms compared to the surrounding planks... makes me think that the beings who built those platforms and stairs and who operate the robot/mecha are very small, like a civilization of mice or rats, for example, and that the surrounding planks of the floor and walls were made by another much larger race/species... but they must be of "normal" size in human terms, unless it's a species of giants who also use giant trees like sequoias or something like that.
Is that "stage" surrounding the robot/mecha some kind of rock formation like those formed naturally