From grim experience, Maziar Bahari knows the fear that is probably gripping eight Iranian journalists who were arrested late last month and taken to Tehran's notorious Evin prison.
Mr Bahari was among the approximately 100 journalists detained in June 2009 during the tumult following president Mahmoud Ahmadinejad's disputed re-election.
The latest crackdown on reporters affiliated with reformist news outlets appears to be aimed at muzzling dissenting or independent voices, and suggests that as Iran gears up for its next presidential election in June, the regime's fears of unrest are escalating.
"My guess is they're all in solitary confinement," said Mr Bahari, an Iranian-Canadian journalist and filmmaker who spent 118 days in Evin, all but 11 of them alone in a small cell.
He suspects that they will be under extraordinary pressure, as he was, to confess that they were part of a western conspiracy to undermine the Islamic republic.
He says that he was beaten, slapped and kicked. As bad as that sounds, it was not the worst abuse he suffered.
"Solitary confinement leaves you with a feeling of utter despair and loneliness. It's the worst kind of torture," said Mr Bahari, 45.
"You don't know who's in charge of your life or what's going to happen to you. But you do know that you're in the hands of a government that has no respect for the law," Mr Bahari added. "And, of course, you know Evin's reputation."
The prison is located in a relatively affluent north Tehran suburb against the backdrop of the snow-covered Alborz mountains. Its picturesque setting belies its place in the dark corner of the Iranian psyche.
As Iran's biggest jail for political prisoners, its very name evokes images of basement interrogation chambers and cramped, one-person cells.
Constructed by the shah
The sprawling, iron-walled complex was built in 1972 during the rule of the US-backed shah, Mohammad Reza Pahlavi. It gained notoriety when members of Marxist and Islamist groups were tortured and executed there.
Evin was taken over by the Islamic revolutionaries who ousted the Shah in 1979. Its infamy continued, as the new regime executed several thousand opponents there in the 1980s.
Evin is rarely out of Iranian headlines. It has a roll call of high-profile inmates, among them insiders of the regime caught in the crossfire of its feuding hardline factions.
This month, one of Mr Ahmadinejad's closest and most controversial aides, Saeed Mortazavi, was held in Evin for two nights.
During his tenure as Tehran's chief prosecutor, Mr Mortazavi ordered scores of journalists, lawyers, students and protesters jailed at Evin - a record that earned him the title, "butcher of the press".
Mr Mortazavi's arrest has been linked to political infighting, not the widespread allegations of human rights abuses against him. It nevertheless demonstrated the escalating intensity of the power struggle in the run-up to elections.
The cells of Evin Prison have seen other Ahmadinejad allies, as well.
Last September, the president's enemies in the country's judiciary jailed his top media adviser, Ali Akbar Javanfekr, for six months.
Among high-profile prisoners in the women's ward is Faezeh Hashemi, a feisty daughter of an Iranian former president, Akbar Hashemi Rafsanjani, a founding father of the Islamic revolution. She is serving a six-month sentence for taking part in anti-government protests and allegedly spreading anti-state propaganda.
Evin also makes periodic headlines abroad.
Nasrin Sotoudeh, a women's rights lawyer jailed at Evin, went on a 49-day hunger strike last year that culminated when court authorities bowed to her demand to lift a ban barring her daughter from travelling abroad.
And there was international outrage in November when a little-known blogger, Sattar Beheshti, was allegedly beaten to death in Evin by Iran's cyber police.
Blindfolds and master's degrees
Given the secrecy that shrouds Evin, human rights organisations cannot say exactly how many prisoners are held there. But one well-connected former political prisoner, who asked not to be identified, puts the number at about 6,000.
"Of these, about 300 to 400 are political prisoners, including between 30 and 50 women," the man said.
With dark humour, Iranians have dubbed the prison "Evin University" because most of its political prisoners are very well-educated.
Several Evin "alumni", like Mr Bahari, a former reporter for Newsweek magazine, have written harrowing accounts on their time there.
"The average level of education in Ward 209 [where political prisoners are held] is a master's degree," said Omid Memarian, an Iranian journalist and rights activist now based in New York.
He spent two weeks in Evin prison in 2004 after being forced to confess to false charges that he acted against national security.
Ward 209, named after its telephone extension number, is operated by Iran's Ministry of Intelligence, which is leading the latest crackdown on journalists.
Most of the ward's inmates are held in solitary confinement. The average cell there measures 2.2 metres by 1.7 metres and is equipped with a small washbasin but no toilet or bed, another former inmate said.
"One of the most serious problems in 209 and 240 is that the lights are on 24/7, so you can't sleep for more than three or four hours at a time," he said. "And you are blindfolded whenever you leave your cell."
Political prisoners still under interrogation are held in both wards. Once convicted and sentenced, most are moved to Ward 350, say rights activists and former prisoners.
This ward has communal cells and is run by prison authorities, rather than employees of the intelligence ministry or members of the Revolutionary Guards.
While no longer in solitary confinement, inmates in Ward 350 complain of other hardships, such as overcrowding, lack of adequate facilities and degrading treatment.
Despite the harsh conditions at Evin, Iranian authorities insist that conditions in the country's prisons meet international standards.
Responding to open letters of complaint smuggled out of Evin, an Iranian parliamentary delegation made a six-hour visit to the prison last month. One of the four MPs concluded conditions in Evin were better than those in US jails.
Another maintained Evin could hardly be called a prison because its facilities were so good.
"From now on, I will call it Hotel Evin," Safar Naeimi said. The quality of food there, he added, was better than he enjoyed at home.
His glowing appraisal drew a tart retort from a leading reformist politician held in Ward 350.
In an open letter, Mohsen Mirdamadi said that if Mr Naeimi was so impressed, he should check into the "hotel" for a stay to acquaint himself "with all its hidden aspects".
Ms Hashemi, the former president's daughter, was blunter.
The "tactless" reports by the parliamentary delegation were a mixture of "lies and delusion", she wrote in an open letter. Mr Naeimi treated the women prisoners he met "with contempt", she added.
'Torture is mainly psychological'
Former inmates say the main problem at Evin is not the facilities, but human rights abuses such as solitary confinement, harsh interrogation tactics, and the denial of phone calls, family visits and access to their lawyers.
Another common complaint is that health care is often insufficient or even deliberately delayed or withheld as a means of pressuring political prisoners.
Mr Bahari said his interrogator often threatened him with execution and he twice "seriously considered suicide" by breaking his glasses and slashing his wrists with the shards.
"The torture in Evin isn't the classic definition like pulling out finger nails or putting your head in a vice," Mr Bahari said. "The torture was mainly psychological. The regime realises this is much more effective than physical torture. With psychological torture there is no threshold of tolerance and the torturer has infinite possibilities."
One form of psychological pressure is to hold political prisoners in wards with hard-core criminals. "A famous journalist I know was put in with an ordinary criminal who threatened to rape him on a regular basis," Mr Bahari said.
Mr Memarian's two weeks in Evin were spent near prisoners on death row. One was a serial killer he feared would kill him at any time - an assault that would prolong his own life because an investigation would be required.
"I could also hear the constant screams from people whose interrogation was not yet over and they were being beaten," Mr Memarian said. "It was terrifying."