The Mechanical City is both a city and a giant Mechanical Creation, capable even of space travel as a spaceship.
Although it possesses autonomous consciousness and can act independently, it also has a Main Control Core.
Theoretically, if the Mechanical City loses control, it can be forcibly "manually" operated using the equipment in the Main Control Core.
The Main Control Core Room is where all the energy and information of the Mechanical City converge, making it easy to control all the city's information from there.
It is also where Su Yu resides, effectively making it Su Yu's "bedroom."
If Su Yu is not elsewhere, the Main Control Core Room is most likely where he is.
Everyone, harboring uneasiness, sets out once more toward the underground core place.
The main control core is very important, hence the strict precautions, mainly by the Mechanical City itself, not allowing others to wander inside.
