The Torturer's Guild is used to enable a pair of torturers to torture criminals with the various torture engines. When criminals are put in dungeon and sentenced by the judge, instead of the judge, a torturer (or two) comes and leads the criminal to the engine and starts rehabilitating him until they purge or die. Several machines used to be operated by two torturers, but now all of them needs only one torturer.
Note that criminals sentenced to wear the humiliation mask and those who are put in stocks and gibbets don't need the torturer's guild. The judge himself will take them to these places and leave them until becoming a law-abiding citizen again.
In their free time, torturers like to talk about their experience and stories of their lives.