The Royal City of the Guardians was not an actual city.

It was the collective name of the Dark Realm's core residential area.

This area sprawled on for millions of kilometers and it was a great basin that was surrounded by shattered peaks. From above, these shattered peaks naturally formed a huge city wall and this was how it came to be known as the Royal City. The Guardians' camp decided to capitalize on this natural barrier and built garrisons there and many intellectual races ...