“One of these fell on me. I didn’t enjoy it” - Corin Hayes
These are secret cities, usually small and set way off the shipping lanes which are operated by the Corporations for their own purposes. Each is different, suited to its purpose, well-guarded, and unfriendly to strangers.
There is a second type of Silent City which the military and corporations don’t talk about. Small, independent settlements which owe no allegiance to a larger corporation. Some are religious centres or retreats, others are owned and run by pirates, some are peaceful collections of Doomsday-Preppers, and some are scientific stations full of (mad - Corin) scientists.