These are usually regional and locale specific. They are for civil and minor criminal transgressions.
These are super secure facilities for the worst criminals and violent offenders.
Although the word “dungeon” is typically just used to denote a built, underground facility – usually into the foundations under a locale – these are the secret prisons as well. Some Dungeons hold all levels of incarceration, but the connotation is used to suggest the worst.
These are the places where the Dominion Codes end (though the lowest level maybe maintain in order to keep a subject alive and allow plausible deniability in event of a death and the boody must be turned over. These are often “known secrets” – everyone knows that they exist, but to press the issue may land you in one or worse. Rendition into a dungeon is often done in secret, with special forces effecting the capture and incarceration.