Tourism does not come more chilling than in the visitor centre at the remains of the Chernobyl nuclear power station. The view from the window is hypnotic in its awfulness. It overlooks what appears to be an unremarkable industrial complex, dominated by a red-and-white striped chimney stack wrapped in a steel frame. Pop music blaring from a radio somewhere within the site adds to a sense of normality that is misleading, shockingly so.
The surrealism of disco sounds in such a place is reinforced by the centre's ominous exhibits. They are dominated by a large model of what cannot be seen from the window. It represents the inside of the wrecked Reactor No 4. Tiny figures in white protective suits are placed among the mock debris, replicating those who today, only a few hundred yards away, perform the most dangerous tasks imaginable.
Beside the display, a video relates what happened at the plant 20 years ago next month, on 26 April 1986. In brief, inexperienced operators in the control room made catastrophic mistakes during the testing of equipment, compounding fundamental design flaws and inadequate safety procedures.
The result was the world's worst - and continuing - environmental disaster involving nuclear energy. One casualty was the company town of Pripyat, little more than a mile down the road. It was home to the plant's workers and their families, until the population of nearly 50,000 was evacuated en masse, as a radioactive vapour descended on them. What they left behind will remain abandoned forever. It is the ultimate ghost town.
There are still scenes, among its poplar-lined avenues and Party symbols of the Soviet era, which capture the poignancy of a hurried escape: a piano in the remains of a 14th-floor apartment; a doll left in the community's nursery where bed-frames line the walls; books strewn on the floor of what was the public library, some date-stamped on the day disaster struck.
As the commentary in the visitor centre puts it: "Like Hiroshima and Nagasaki, Pripyat was conquered by the atom." The film ends with the message: "The Chernobyl problem is still unresolved." The changing red numbers on a digital panel are part-confirmation of that. On the day we were there the figures were darting between 1.21 and 1.17, and back again.
Julia Marusych, head of the information department at Chernobyl and the woman with possibly the toughest public-relations job on the planet, explained what the numbers meant. They represent, in milliroentgens, the level of radiation outside the centre. 1.21 did not seem a lot, I suggested, and she agreed, before making the point that modest or not, it is still 100 times more than the average natural level of background radiation.
Inside the perimeter fence enclosing the vast redundant plant itself, so-called "stabilisation crews" monitor what is going on at the heart of the site now. It is perilous work. Censors indicate that radiation levels at the reactor's core are 300 million times greater than normal safety margins.
Devastating though the explosion and fire were in 1986, only 3 per cent of the reactor's lethal cocktail of radioactive material escaped at the time - sufficient, however, to lay waste to parts of northern Ukraine, and contaminate 70 per cent of neighbouring Belarus.
Two decades on and more is now leaking into the atmosphere through large holes in the concrete sarcophagus that was built to encase the reactor. Experts said at the time that the protective structure would have to survive far longer than the pyramids of ancient Egypt, such is the long-term potency of radiation.
The present structure has proved inadequate and only now, after years of argument, is work scheduled to begin on what is hoped will be a permanent solution. In the meantime, how safe is the site, which, remarkably in the circumstances, drew 2,000 visitors last year, many with a scientific interest, but also those classed as "disaster tourists"?
The spokeswoman doesn't know. No one does. "We cannot say conditions are safe," said Julia Marusych. "Risks remain." How secure is she in her cheerful, modern office when it overlooks the menacing complex which emits such a deadly and invisible poison?
How is her health? She shrugs. She feels fine, but after working there for six years...
Officially the disaster claimed 56 lives, mainly among those who fought a heroic battle to contain it. Doctors and others are in no doubt that the true figure is already into the thousands as the long-term effects of radiation take their toll. Cancers in various forms have soared, as has the number of children being born with deformities.
Humanitarian aid groups in western Europe do what they can. An Irish-based charity is at the forefront, providing respite for the terminally ill, helping to pay for life-saving operations, and giving money and practical support to impoverished, state- run institutions which will struggle to cope with the human cost of Chernobyl for generations to come.
The charity's founder, Adi Roche, has been to the region about 50 times, and visited the plant itself on eight occasions, putting her own health in jeopardy. She believes the risk is justified in promoting her anti-nuclear stance, all the more relevant to her now that Britain is considering an energy policy ever more reliant on nuclear power.
With its greatest calamity looming behind her she said: "We are in the middle of madness here. Chernobyl represents the first large-scale 'experiment' in the management of a nuclear crisis, and it has failed miserably."
Her opponents include Viktor Krasnov, director of the Department of Nuclear Radiation Safety at Chernobyl, where he has worked for 14 years. He talks optimistically about the situation there, despite the fears of some experts that the reactor's core could implode, causing even greater devastation than before. "There is no immediate danger," he insists. Krasnov is also confident about the sarcophagus, despite its leaks through a decaying shell and the fact it will be relied upon for at least six more years before a new protective shield is constructed. "The situation is under control. It is absolutely safe."
He has not lost faith in nuclear power. On the contrary, he thinks it was a mistake to abandon Chernobyl's other reactors. If he had his way Chernobyl would still be generating electricity in support of Ukraine's four other nuclear plants, and helping to reduce reliance on politically vulnerable energy supplies from Russia.
Krasnov's view is that the lessons learned at Chernobyl have reinforced the industry as a whole. He added: "I am absolutely sure that such an accident will never happen again. Nuclear energy is safe."
You do not have to travel far for contradictions. The scene is a vehicle graveyard where 2,000 contaminated relics - former Soviet helicopters, army trucks and tankers, fire engines, ambulances, buses and cars - reveal the scale of the so-called Battle of Chernobyl. In the words of a retired Army colonel who ruined his health in flying numerous sorties over the site during the emergency, it was nothing less than a battle "to save the world" from unprecedented amounts of fallout.
The wreckage is kept in a guarded compound while the authorities decide what to do with it. After 20 years, answers remain elusive. In the end it may join more heavily contaminated equipment and have to be buried.
Such desolation also exists in a different form 100 miles and more from Chernobyl. Radiation pays no heed to national borders. In Belarus, exclusion zones contain numerous villages emptied of life because the land is dangerously irradiated, and will remain so for centuries. Their names have already disappeared from updated maps.
Where bulldozers haven't already removed the past, wooden and brick houses look forlorn as they collapse bit by bit and are embraced by the vegetation of an apparently normal landscape, dominated by forests of pine and silver birch, and almost devoid of human activity. Yet for those who can obtain the documentation to venture into these beautifully desolate areas, there are a few signs of habitation.
Take the case of what once was Komsomolskya Street, in the hamlet of Bartolomeevka, in Belarus. At No 23, the electricity is cut off, the postman never calls and officialdom has ceased to recognise its existence. This is the home of Ivan and Lena Muzychenko, an elderly couple who refused to leave and now survive through their chickens and hens, and the food they produce in their polluted garden. "It is better to die from radiation than hunger," they say.
A handful of others have, against all advice, returned to the village. One local man, Nikolai Gordunov, was evacuated in 1991 to a "safe" town far away across the country. After three years he could no longer tolerate what he calls "balcony life" in an urban apartment and chose to return to the contaminated countryside where he grew up. Sharing the risks with him is Svetlana, the woman he met and married while in exile.
Chernobyl wiped out numerous villages in 1986 despite the valiant efforts of 600,000 people, many of them volunteers, who risked their health - and in many cases gave their lives - to "clean up" the polluted land in the days, months and years afterwards. They were the so-called liquidators, or likwitators.
Few were braver than retired Soviet colonel Oleg Chichkov, now 65. At the time of Chernobyl he was flying army helicopters near the Chinese border. He recalls reading a "tiny article" about an incident at a nuclear power station across the continent. "They'll soon have that under control," he said to himself. Shortly after, he and a few colleagues were ordered there immediately. From Chichkov's military training and knowledge of nuclear power he was under no illusions about what was at stake.
In his MI26 helicopter, supposedly protected against radiation by its lead-covered floor, he and other pilots between them flew 60 sorties a day for more than five weeks above the site. Chichkov was 45 then and had three children. Although the pilots were given iodine pills, he understood the perils of radiation and refused to expose younger crews who were not yet fathers to the risk of becoming infertile. Of those who shared the missions with him, four are now dead, and his own health is deteriorating.
He has had a stroke, suffers from a bone disease, and walks with a limp. He retains his military bearing however. His uniform is ablaze with medals, one of them for service at Chernobyl. But on a practical level life has been tough since the collapse of the Soviet Union and what he describes as the resulting "mess".
A grant covers half the rent on his apartment, he receives a state pension equivalent to about £25 a month, and once a year has a paid-for spell in a sanitorium. He has another perk as well - the man who helped "to save the world" is entitled to travel free on public transport in Minsk.
Not only has his own health suffered. His wife, Natasha, had thyroid cancer, one of thousands of such victims whose condition is marked by a post-operative red crescent scar across the throat known locally as the "Chernobyl Necklace".
Life has changed in other ways for Igor Avetisov. He lived in Uzbekhistan, more than 2,000 miles away, when he was told that his driving skills were needed at Chernobyl. He was flown to Kiev with 120 others - including friends, many of whom he says died prematurely. They arrived at Chernobyl nearly two months after the explosion, and even then they were not told how dangerous the situation was.
He remembers seeing an army of people washing down the roads in a near-hopeless effort to keep the radioactive dust down in the summer heat. He also recalls driving near Pripyat and other places where one minute there had been everyday normality, the next only clues to indicate vanished lives that would never be restored. "In the gardens, washing was still on the lines. In a shop I saw sausage on the scales, and money that had not been locked away. It was kind of scary."
Avetisov is 70 now, with a smile dominated by his gold tooth. He is surprisingly cheerful considering that his poor health has exiled him in Belarus for the past 16 years. He is both angry and philosophical, proud too to have a medal which records that he was "a participant in the liquidating of the consequences of Chernobyl nuclear power plant".
He did return to his distant homeland for a while but because of his lung disorder doctors there advised him to live by the sea or near pine forests. A relative offered to care for him, though it meant returning to a country which, for all the official assurances, continues to pay a huge environmental and human cost.
This is confirmed by scenes at Vesnova, a state-run institution in the countryside south of Minsk. It is part orphanage, part unit for severely handicapped children and young people. It is home to 138 victims, aged four to 25, and the director is in no doubt that in many cases physical and mental abnormalities are linked to their mothers' exposure to radiation and its genetic consequences.
Several of the children were abandoned by their parents because they lacked the resources to cope. Countless other families struggle to care for their sick children at home, despite the hardships and minimal state support. Charities help alleviate the suffering - which in some families has affected three generations since the disaster - by providing drugs, nursing care and other forms of help.
Despite Chernobyl's tragic toll - a 2,400 per cent increase in the incidence of thyroid cancer, 250 per cent increase in congenital birth deformities, 100 per cent increase in cancers such as leukaemia, plus heart disease and a soaring suicide rate, according to one charity - Soviet-style persecution is being inflicted on those who speak out. The most famous dissident is Professor Yuri Bandazhevsky, former rector of the medical institute in Gomel. He went public after noting an alarming increase in heart problems and birth defects among children after Chernobyl.
As a result he was hounded by the secret police and removed from his post. He continued to challenge the government line and in 2001 was jailed for eight years with hard labour on trumped-up bribery charges. He was adopted as a prisoner of conscience by Amnesty International and eventually released in 2004.
Even so, he remains under virtual house arrest and risks further punishment for continuing his work. He also has a personal incentive. His wife, Galina, has had her thyroid and womb removed - cancers that he attributes to the disaster.
Their apartment in Minsk also serves as a makeshift laboratory where the professor researches the effects of radiation on animal foetuses, notably those of hamsters, which have a genetic print similar to that of humans.
Unsurprisingly he is a fervent opponent of nuclear power. So what is his message to Tony Blair as the British government considers building more nuclear plants?
"To those sitting in offices, debating this issue, I have this simple message: to want more nuclear power rather than less is madness. I wish I could show these people what I see in mortuaries in my country. I wish I could show them the horror of what my experiments reveal. I would say to them, 'Do you need further proof?'