The city was called Vox and it was surrounded by quite a few floating islands. However, rather than monsters occupying the islands, they managed to obtain the islands for themselves and arm it with ballistas and soldiers with flying divinities so that they could keep the monster at bay.
Not only that, but the city was also surrounded by large stone walls with metal gates. The gates weren't closed and anyone could enter at will but there were guards stationed everywhere.
Glancing up at the top of the walls, Shiro could see mounted weapons and tens of guards standing at attention. From what she could tell, each of the guards were performing their duties magnificently as none of them were slacking.
Back on earth, Shiro had seen guards who would only stare off into the distance and daydream but these guards were like hawks. Every subtle movement they saw would be checked to be sure that there was nothing suspicious.
