The city was simply known as Fourth Heaven. As the center of the Fourth, it was a hub of tourism and business. Of course, those that could enjoy it were very few in number to begin with. With the sheer size of the Fourth Heaven, even the First, Second and Third Heavens combined couldn't match up to it, and crossing the wilderness was something those beneath the Sky God Realm wouldn't dare to do.
As such, though there weren't any rules about who could and couldn't enter the city, it effectively became a highly elitist region where only those who could afford teleportation or had seniors in the Sky God Realm, or were Sky Gods themselves, could make it to this place.