Royal Palace, underground.
This is an unexpectedly spacious area.
For it contains many secrets the Kingdom cannot disclose to the public.
Of course, the "not to be disclosed" referred to here is not something dark or forbidden, but just as it is said, purely because of its secrecy.
For example, important magic research institutions of the Kingdom are located here, and so are the sources of the barriers defending the Royal Capital and the Royal Palace. Should any suspicious person enter here, it would be quite detrimental to both the Kingdom and the Palace.
Therefore, only privileged personnel designated by the Royal Family have free access to this place. Other than them, even high-ranking nobles and knights aren't allowed inside. The security is exceedingly stringent, with the Knight Order patrolling the same spots every few minutes, and key facilities are guarded by armed forces at all times, making intrusion nearly impossible.
