Maghaberry Prison is changing.
In the narrow corridors of one of the old blocks, the sight lines were poor. It felt labyrinthine, confined, confusing.
Gates checked movements at regular intervals, keys hung from warders' belts.
In this 30-plus-year-old building the surroundings were clinical, with pale green painted corridors and rows of cells with observation shutters for guards on patrol to peer through.
The older houses close in June next year; at the other side of the prison construction was ongoing on a brand new unit.
Its cell blocks were named after rivers that flow through Northern Ireland, such as the Quoile, Erne, Bann and Bush.
Maghaberry holds more than 800 prisoners and faces unusual challenges.
Within its walls and barbed wire fences live republican and loyalist paramilitary inmates, where tensions have boiled over in the past, as well as those convicted of serious non-terrorist offences.
Its warders have been targeted by dissident republicans: David Black, 52, died in a motorway shooting as he drove to work there, and prison officer trainer Adrian Ismay, 52, died from bomb injuries in 2016.
The jail also houses "trusted" prisoners who perform a variety of roles within the jail and some are preparing for release back into the community.
Previous scrutiny reports have highlighted the challenges of housing ordinary and paramilitary prisoners within the same complex.
The Prison Service has taken steps to address that, including moving female inmates to a separate centre at Hydebank.
A recent report acknowledged that significant improvements had been made at Maghaberry and the banter exchanged between officers and inmates was easy.
In one of the veteran houses newly admitted inmates were milling around, not yet part of the structure of prison life but generally busy cleaning, tidying, or training at a gym.
One new prisoner was preparing to change cells, packing his stuff on his bed.
He was effusive in his praise for arrangements which allowed him contact with his family.
The inmate said: "We are just so grateful."
The physical contrast with the new buildings was marked.
One featured a spacious "hub" from which the wings radiated out. Prison officers shared the landings with inmates.
Governor David Kennedy said: "You can see and hear everything going on and staff are very easily accessible."
More vulnerable prisoners were held upstairs, in a dedicated area.
There was a restorative justice landing where victims and their assailants were brought together behind bars, a mechanism for dealing with conflict and low-level issues in the prison.
Mr Kennedy added: "Just because two people don't get on because of what happened previously, it is important that we get them working together."