The Hallowtree Penitentiary
The Hallowtree Penitentiary is one of the more harsh prisons in the world. Albeit a step below Crimin-Isle itself, it still boasts both incredible security, as well as a deterrence to severe magical crimes on account of its unique system of punishment. Keeping most of the high-level prisoners at bay are beings of negative energy (typically wraiths) that keep the prisoners at a low strength. Low enough to deter any attempts at escape, or hope of escaping in general.
The only two entrances of the penitentiary are from the Runeguard's HQ itself, or the prison dropoff platform within the bounds of the university's protective dome. Prisoners delivered in this particular entrance are brought in by The Tritone; a massive prison ship built many years ago by the original Bannermanes themselves.