When Bill Brodie organised a study tour to Berlin for GCSE history and A-level German pupils from Antrim schools his one anxiety was that by focusing on the Nazis and the war, the students might come away with an unbalanced, purely negative view of the country. To his horror, during the first day’s coach tour of the city the guide delivering an overview of German history halted at Hitler. Three times he tried to begin to explain the atrocities meted out in his name. ”. . . Well, he was Austrian,” was all he could muster.

It was a moment of supreme irony, of course, for this side of the English Channel far too many people still believe the rise of the Nazis could only have happened over there because they are German. But in fact it opened the Pandora’s box of questions which history students should thrive on. Was there a holocaust? Did the Germans know? Did they try to stop it? How were the Nazis able to hold on to power for so long? What were the consequences? Searching for the truth involves a disturbing exploration of the the darkest side of human nature.

For the Ulster pupils, drawn from schools under the aegis of the North-Eastern Education and Library board, for which Bill Brodie is a modern languages adviser, the first answers came at Plotzensee Prison. Now a juvenile detention centre, during the Nazi era it was one of the largest jails in northern Germany where 2,500 men, women and youths were guillotined or hanged for standing up against Nazi breaches of human and democratic rights.

As the number of death sentences mounted, a massive iron beam with a row of hooks fixed to it was installed in the small execution chamber so that prisoners could be hanged in quick succession like butcher’s carcasses.

A thought-provoking guide book, Plotzensee Memorial, provides detailed accounts of how the Nazis set out to crush attempted resistance by political groups and even senior army officers and persecuted the Jews. It quotes Heinrich Himmler addressing SS generals in Poland in 1943 on the subject of exterminating the Jews, saying: “Most of you will know what it means to have 100 corpses lying there, or 500 or 1,000. To have seen this through. . . is a page of glory in our history which never has been and never will be mentioned. ”

Himmler was head of the SS and the Gestapo and it was from his and neighbouring offices on Prinz-Albrecht Strasse that the advanced industrialised production of death, otherwise known as the Holocaust, was directed. The offices were razed to the ground by Allied bombing raids, but historians have recently excavated cells at what became the most feared address in Germany - where prisoners were tortured until their spirit broke. They have also built a small modern exhibition centre to provide written and photographic documentation of the work of the mass murder executives, who from their desks planned the systematic extermination of Jews, Gypsies and others deemed undesirable, such as the mentally handicapped, in an attempt to achieve racial purity in the Third Reich.

Many of the photographs are powerful images - hungry faces of hounded Jews staring out under felt caps; bodies slumped on the ground beneath the pistol fingers of German troops; steely-eyed portraits of SS officers. But the words are only in German and of little value unless you are accompanied by language students.

We learned more from a talk and discussion with Klaus Hesse, who describes himself as “a scientist, a historian” and is willing to talk to groups if an appointment is made. He said there was a silence on the theme of genocide in Germany for about 20 years after the war. “Then the next generation began asking their parents what was their role in the war and now there’s a more critical handling of it.”

The first gas chambers were mobile and were an attempt to find an alternative to shooting, he explained. As the Germans occupied more lands in Poland and Russia in the East they had millions more Jews in their territory and shooting was proving too expensive and stressful on the soldiers as they tried to wipe them out. “I think most Germans did not really know what Auschwitz meant, but soldiers from the eastern front told people in letters or when the came home on leave. About 400,000 people had the possibility of direct contact with mass exterminations and maybe one million had contact to the truth as rumour. But the deportations took place in daylight and the Germans were told that they were going to the East to work,” he explains.

So did they do anything about it? Some answers can be found at Sachsenhausen concentration camp, situated on the edge of a Slavic town, to the north of Berlin. “This will not be a laugh,” Heather Thompson, a history field officer from Antrim, advised the pupils on the coach. “This will be a very sobering experience for all of us. In Plotzensee they killed after a show trial. Here they killed when they wanted - Jews, clergymen, trade unionists.” More than 100,000 died there in fact.

Sachsenhausen on a grey winter’s afternoon, is a desolate place. The landscaped driveway hides the camp’s menacing purpose from the outside, though I doubt the sickly sweet smell of burning bodies could have escaped local residents when the ovens were used. Through the inner gates you enter the vast parade ground where up to 33,000 prisoners at any one time were forced to watch their fellow inmates being hanged or abused.

Here was industrialisation gone mad. At one side there are rectangles of broken tarmac where inmates had to march up and down for ten hours at a time with 35lb weights on their legs to test the usefulness of different types of shoe sole. In the canteen in the middle there is what can only be described as a museum of suffering, where exhibits include clumps of hair, a by-product from live and dead prisoners that was used to stuff cushions; gold fillings that were melted down to boost the Reich’s earnings; and a can of the poisonous pellets used to gas millions.

In one gruesome corner of the camp, you can, if you can stomach it, go into the pathology laboratory and mortuary, and walk right up to the table where medical experiments were conducted on inmates. On a couple of walls are pictures of severed torsoes and tattooed skin that was used to make lampshades. It might seem like shock tactics, but it is an important reminder of the depths to which organised society can sink.

In the middle of the vast, silent, grounds of the camp stands a monument to the 18 categories of prisoners who died here, from dissidents to Jews. But it did not stop when the war ended - 20,000 Germans were put to death after the Russians took control, though their bodies were disposed of less efficiently in the nearby woods.

Therein lies the tragedy of half a century or more in Berlin. The same pain visited on its people by Hitler’s totalitarianism, the Allied bombs, and confrontation with guilt after it ended, was recycled in another form under Honecker’s Communism through economic hardship and political repression.

These days Berlin is a building site. Crane city. In the centre, especially near the path of the fallen Wall and one-time dead-man’s corridor, every other street seems to be blocked off due to construction work in the race to rebuild. Allow extra time to negotiate the mazy one-way systems that result, if you want to visit the Checkpoint Charlie museum. It is worth it to see the impressive range of escape vehicles - Beetles with hidden compartments, a flying machine, an old bread van lined with concrete to prevent bullets getting through - and the stories, some tragic some happy, of those that tried to make it to the West. As much ingenuity was put into these contraptions as the Nazis put into death machinery. The museum also puts on a good range of video documentaries (in German) on the fall of the various east European Communist regimes to people’s movements.

Potsdam, just the other side of the Glienicker Bridge where Cold War spies were once swapped, is a good starting point for examining the consequences of the war. The Schloss Cecilienhof houses the conference room where Churchill, Stalin and Truman redrew the map of Europe and is put into its historical context by a video documentary (in English) which can be viewed by the entire group. But perhaps more interesting is the crumbling old town, where abandoned terraces stand, still pockmarked with bullet holes from the last days of the Nazis. Whole streets wear the colourful graffiti of their squatters like a tide-mark of the receding Soviet empire, as they wait for their owners, many driven out under Hitler, to be traced or established in court. Berlin and Potsdam, will always provide a fascinating focus for studies of the rise of the Third Reich, the Second World War and the Cold War. But now is the best time to go, before the visible consequences of Hitler and Honecker’s reigns of terror and the differences between East and West are buried by the developers; and, while there are still survivors of the SS to talk to and life under a Communist dictatorship is still fresh in the minds of those who endured it.

Was Sachsenhausen too much to cope with? Emma Woods, 17, said: “Coming face to face with it was a shock, but I’m glad I went. GCSE was just skating over the surface. This makes our problems back home seem tiny.”