It doesn't look like much from the outside, 45 Novoslobodskaya Street, just another charmless building on a main road leading north out of Moscow.
Indeed, I passed it several times a week for many years before realising what lay behind its cheap brick facade.
Butyrka was built in the 18th Century during the reign of Catherine the Great and remains to this day one of the most notorious prisons in Russia.
And that, believe me, is no small claim to notoriety. For many here the mere mention of its name induces a shudder of fear.
From the outside it's just another drab building
Butyrka has become a powerful symbol of all that is wrong with the Russian prison service.
More than 200 years after they were built, the
original cells are still in use - dark, dank, rancid and horribly overcrowded.
The notion of privacy does not exist. The cells were designed to hold 20 men - bad enough one might think - but in many cases contain up to 80.
Conditions are so bad the inmates have to work a
shift system to get a sleep. They share one toilet and one shower.
The prison was until very recently home to some 5,000 inmates.
Some 37,000 inmates of Russian prisons are known to be HIV positive
Improvements in sentencing policy and amnesties
have reduced the number to below 4,000 but what is most astonishing of all about Butyrka is that the vast majority of the inmates have not been brought to trial.
The prison is what is known in Russia as a SIZO, a pre-detention centre.
But Butyrka makes a mockery of any presumption of innocence.
Once inside its walls, the chances of getting out quickly are remote indeed.
There are some who have been inside for five years, still waiting for their cases to be heard.
TB and Aids
Disease is rife in Russia's prisons.
The overcrowded insanitary conditions
have become the spawning ground for a dangerous, drug-resistant form of
Entering cells can be tantamount to receiving a death sentence.
In a prison in Kaluga 100 miles south of Moscow, I spoke to a man who had been imprisoned for three years for stealing a sack
Russian prison inmates often have to sleep in shifts
He'd entered prison a healthy man but now had TB and feared for his life. There are thousands like him.
The awful truth is that an astonishing 10% of this country's prison population has the disease.
Now HIV has begun to rival TB as a threat.
Homosexual sex is a fact of prison life. Staff in some prisons are alert to the threat and issue condoms and lubricant to the inmates but others refuse to recognise the problem.
Drug use is also widespread. A survey of Russian prisons cited by the WHO last year found that of a sample of 1,087 prisoners, 20% had injected drugs in prison and that 64% of those shared used needles.
Some 37,000 inmates of Russian prisons are known to be HIV positive.
But there is at last a ray of hope even in this the darkest of places.
Change on the way
The Justice Ministry appears genuinely committed to reform and, astonishingly, Butyrka is at the forefront of the changes.
Last July saw the introduction of a new legal code that, on paper at least, enshrines the presumption of innocence at the core of the judicial system.
Practice still leaves huge amounts to be desired, but changes are happening.
When I first came here I was struck by the good humour of the prisoners living in those conditions - in Britain, we'd have had a riot within a day
Terry Bone, head of UK exchange project
For the first time in several years, the prison population has fallen below one million.
Not much to shout about when the USA is the only
country in the world with more prisoners per capita but still a step forward.
The biggest changes are happening in the SIZO prisons.
The number of pre-trial prisoners was reduced last year by 70,000 to 190,000 and new legislation limits the amount of time an inmate may be held in a SIZO without a hearing to six months.
The man behind the changes is the deputy Minister of Justice, Yuri Kalinin.
It is he who first invited the British-based International Centre for Prison Studies (ICPS) to become involved in Russian prison reform.
Terry Bone is the head of a four-year exchange project between British and Russian prisons.
He has a lifetime of experience in the UK prison service behind him and was deputy director of prisons in North Region at the time of the riot in Manchester's Strangeways prison in 1990.
He had the task of bringing things under control. But he had never seen anything like Butyrka.
"When I first came here I was struck by the good humour of the prisoners living in those
conditions. In Britain, we'd have had a riot within a day."
And struck too by the immensity of the task facing the reformers - and their commitment.
He has witnessed some astonishing changes - not least in the SIZOs.
Russian prison officers make regular visits to prison training centres in UK and are coming away with a new perception of their role - although they're not entirely impressed by the decrepitude of many of Britain's own prisons.
Paint peels from the 200-year-old walls of the Butyrka
Some of the changes are the direct result of the ICPS's advice.
Until very recently, shutters completely blocked out daylight from all SIZO cells.
Now they've been removed - with immediate consequences for the psychological atmosphere in the cells.
Prison officers say tension and stress are much reduced.
Lieutenant-Colonel Karen Avyetisian is a dapper Armenian who rules the corridors of Butyrka with an iron - albeit mostly benign - hand.
When I met him he was wearing US army camouflage fatigues bought on the black market.
"Courtesy of the Georgian army,' he explained.
"They get them from the Americans as
part of an aid programme then sell them to people like me in Russia."
He laughs easily and smokes with an elegant flourish of his gold-tipped cigarette holder.
About 20% of the prison has been modernised in the last year at a cost
of some $2m. The rest is due to be complete by the end of the year.
What that meant, he said, was 20 to a cell instead of 40 and more, cleaner conditions, regular health checks, including X-rays for TB and proper respect for the human rights of prisoners.
The Council of Europe notes improvements but says more needs to be done
He gave a demonstration of what this meant in practice.
On a tour of the new cells (the first we entered had 29 inmates not the so-called 20 maximum), three prisoners complained that they hadn't been given their lunch.
Orders were barked out and within 10 minutes the meals were duly delivered. Would he have behaved in the same way if I hadn't been there?
What is indisputable is that conditions in Butyrka at least are becoming vastly better.
The number of prisoners is down by 800 on last year and efforts are being made to clear inmates more quickly through the system.
But huge problems remain.
The training of staff is inadequate and
attitudes to the prisoners are based on an assumption of guilt - despite the
fact that they have not been brought to trial.
Across the system as a whole, funding remains wholly inadequate.
Prison staff in Moscow are paid less than $160 a month - so little that the authorities have to recruit outside the city. Muscovites won' t work for such small amounts.
As a consequence, they are easily corrupted.
The Parliamentary Assembly of the Council of Europe has acknowledged the changes but says far more needs to be done to bring Russia up to European standards.
And it has singled out the SIZOs for particular criticism - noting the vulnerability of inmates to ill-treatment and torture.
This is all indisputably true.
But what is also the case is that for the first time a beam of light is penetrating one of the darkest corners of Russian life.