It is, cleaner Sahil Kumar says, a rather unsettling place to work.

The rats don't bother him, he has seen plenty of those before.

It's not even the pigeons writhing on the ground, shred to death by the razor wire high above.

It's the ghosts.

If you ask the people who continue to maintain The Rock since it closed for good in 2011, the old Mt Eden Prison is haunted.

There is a lone loudspeaker that continues to crackle and moan, despite the PA system being shut down five years ago.

An electrician was called in to investigate. He cut all the wires leading to it, but the disturbing sounds still echo through the empty hallways.

It's unsettling. But another of Kumar's stories is even more so.

Crouched down in a cell hard at work, a contractor brought in for emergency repairs swears a Maori inmate appeared behind him and yelled, "get the f... out".

By the time the contractor scrambled to his feet, the man had disappeared.

The contractor sprinted out of the prison, and refused to return.

Just the other day, Kumar says, a colleague needed to head in to the old prison at night to check on something.

"I've never seen anyone so loaded down with torches, he was shining like a lighthouse."

Built more than 150 years ago, the imposing fortress was constructed in a style designed to instil fear in those sent there to serve time.

A panopticon prison with spokes radiating from a centre hub, it was the site of dozens of executions, including New Zealand's last hanging in 1957.

Since The Rock's doors were shuttered in 2011, its halls have remained deserted - save for the semi-regular maintenance to keep it from falling completely apart.

Weeds rule the entrance and shadows creep along the walls.

Row upon row of spartan cells stand empty. The cracked toilets and rusting bed frames are all that remain.

Unknown to most even before the prison was closed, Mt Eden features floor-to-ceiling murals painted by artistic prisoners.

What used to be the visitors room is dwarfed by giant images of sea creatures, including a pair of scantily-clad mermaids deemed too erotic by some staff.

In another area, a mother sporting a moko and carrying an infant on her back watches forlornly over an empty wing.

Outside, razor wire and water cannons continue to stand watch over graffiti-littered exercise yards where prisoners not only stretched their legs but often sorted out their differences.

While guards stood watch above the prisoners outside, the violence that broke out was often finished by the time staff arrived to intervene, he says.

Auckland's Southern Motorway also snakes almost directly above the yards and after its construction, contraband would be thrown from people in the passing cars, despite the mesh wire hanging overhead.

"When they built the motorway we had a series of towers that had armed sentries with rifles. On one particular occasion I was standing there, I hadn't been working here very long and that was usually where you got put, sentry duty, a car pulled up, said g'day to me and threw a tennis ball into the yard and I thought 'do I shoot them or not'?

"The chief officer when I reported said 'certainly not, the things wouldn't fire anyway'."

A trip into the bowels of the building leads to the kitchen, still home to dusty, hulking industrial mixers and ovens.

Just beyond the kitchen, two sets of three holding cells face each other. They were the last stop for prisoners before they were sent to the gallows erected against a stone wall outside.

Lister says prisoners were taken down to the holding cells about 48 hours before the appointed hour and put on "death watch".

Prison staff would sit with them right up until their execution, trying to keep them calm with games of cards.

Just before, the prisoner would be weighed and the hangman brought to the cell, peering through a peephole to make sure he had their size and weight correct.

"The cell would be unlocked, the prisoner would be pinioned either with their hands to the front or the side, they would be steered out of the cell and right outside would be the steps to the gallows."

All 36 executions carried out at Mt Eden would have been traumatic for staff and often a stiff drink would be handed around by management.

"It was a very, very nerve-racking and horrible situation for all the prison officers."

Today the holding cells remain, but old gym equipment occupy the space where the gallows used to be.

The prison originally consisted of a timber stockade built in 1856, and the opening of another building on the site in 1865 allowed the crumbling gaol on Auckland's Queen St to be demolished.

Mt Eden's stone wall, well known to Aucklanders, was built by prisoners using volcanic rock from a neighbouring quarry and completed in the mid 1870s at a cost of £1800.

In 1888 the main building was considered ready to accept its first residents and the final structure was finally completed in 1917.

But even before it was finished there were rumblings it should be closed.

Views about how to incarcerate prisoners were changing and in 1951 the Government bowed to public pressure and announced Mt Eden would be demolished.

This promise was not to be kept, however, with a shortage of funds postponing plans.

In 1965, an infamous riot, which lasted 33 hours and was sparked by a botched escape attempt, left the building in ruins.

At 2am on July 20, 1965, two prisoners attempting to flee were discovered by an officer.

The pair clubbed the officer, took two hostages and started releasing other prisoners.

Fires lit by the excited inmates, fuelled by whatever they could find, including furniture and prison records, quickly spread throughout the premises.

Firefighters sent in to douse the blaze were pelted with bricks and they quickly withdrew.

A decision was made to surround the prison to prevent escape and wait the prisoners out.

After the prisoners surrendered little remained apart from the shell of the building. The chapel and 61 cells were destroyed.

It was one of the toughest prisons in New Zealand and daily life was far from calm.

Over the years it housed some of the country's most notorious criminals, including serial escaper George Wilder and samurai sword killer Antonie Dixon.

Former Mt Eden manager Neville Mark is frank about the challenges of running such a foreboding facility.

"I think to live in a place like this you had to be quite hardy, there was a lack of heating and there were some hard nuts in here too in terms of their sentences, and of course there were some staff who were very similar to that too, and occasionally you had your clashes."

The design of the prison, with all its nooks, crannies and confined spaces, meant there was often punishment dished out away from staff eyes.

But despite the danger, the prison was respected by both prisoners and those who worked there.

"The staff enjoyed working here, even though the walls would sort of run with water in the peak of winter time and things like that, they seemed to be a family and help each other.

"Prisoners had a respect for this place and for some reason they believed you had moved up in something when you were actually in Mt Eden, and that's why it was called The Rock. Both staff and prisoners called it The Rock."

The building has category one heritage status, and demolition is prohibited.

Its location is also problematic, immediately next to its replacement prison and there are security concerns.

A railway line borders the north wall and a motorway the east, making access and parking difficult.

But to leave a building of such historic and architectural importance empty seems a waste, and Corrections agrees.

It's seeking a partner to conduct a feasibility study into possible uses for The Rock, leaning towards the option of turning it into a museum similar to what has been done in Melbourne with the old gaol and San Francisco's famous Alcatraz.

The popular suggestion that it be used as accommodation has been ruled out, with too much red tape and work needed to make it fit for living.

Then, of course, there's the issue of the ghosts.

Would that be an attraction to the public, or scare them away?

Mark is unsure, but he has heard all the stories and won't rule out the possibility Mt Eden remains inhabited.

"The place had been blessed a lot in regards to those feelings and events but it appears it's still happening now since it has been closed down. Staff have heard pianos being played, telephones going and lights going off and on. I've never been able to substantiate that but it's come from a number of people, a number of staff and nobody can explain that.

"The silent, unsaid word around this place is definitely 'haunted'."