B-City

B-City (B市 B Shi) is a large city located on the world's super-continent. This city was briefly seen when the Brain and Brawn Brothers headed there in their quest to rule the world. Before being able to destroy the city, they were defeated by Saitama, but the latter's punch sent Marugori, the giant, falling on the city, demolishing it in his fall.

Saitama Introduction Arc
After Saitama defeats Marugori, his corpse accidentally lands on the city and destroys it.

Rumored Monster Arc
Lightning Genji mentions the city is still being repaired after Marugori's attack.