Six years from now, the Berlin Wall will have been down for as long as it was up. This will seem remarkable to those who grew up in the 1960s and 1970s and for whom Walter Ulbricht's "anti-fascist protection barrier" was a fixed presence. It became the manifestation of the Iron Curtain that Winston Churchill foresaw in 1946 and there was no reason to suppose that it wouldn't last a lifetime, or longer.
I was last in Berlin 20 years ago, just after reunification, two years after the wall had fallen. I had arrived on an overnight train from Munich and spent the morning wandering around the district of Friedrichshain, formerly in the east. The sky was white and still, reflecting the unnatural quiet of near-empty streets. Brutalist apartment blocks built from prefabricated concrete blocks pockmarked the landscape. Two decades on, the silence and emptiness of Berlin's eastern districts remains striking. If there really are three and a half million Berliners, I'm not sure where they are.
Yet towards the city centre (Mitte), the transformation is apparent. Either side of the snaking River Spree, Berlin has become the plaything
of international architects. More than a third of the city's buildings were destroyed during the Second World War. Although some of these have been restored, other areas flattened by Allied bombs have been reinvented. Potsdamer Platz is one; the square in front of the Brandenburg Gate is another.
Transparency was the guiding principle of urban reconstruction in the 1990s. Charlotte Frank's and Axel Schultes's Chancellery building, with its circular openings on either side, is a good example of this, as is Norman Foster's glass dome for the Reichstag. Equally symbolic is the structure of the nearby Paul-Löbe-Haus, where the offices of all 620 parliamentary representatives are visible from a public walkway. There are no blinds or curtains and the offices nearest to the walkway are within reach of an outstretched arm. The 1950s neoclassical apartments along Friedrichshain's Karl-Marx-Allee (known locally as Socialist Boulevard) provide a compelling counterpoint to these late-20th-century architectural adventures.
Berlin today - old and new, east and west - is best seen on foot or from a train on the elevated S-Bahn railway. Those wishing to indulge in Ostalgie (nostalgia for the German Democratic Republic) best avoid the underwhelming and overcrowded Checkpoint Charlie. Instead, visitors should head to the hands-on DDR Museum on Karl-Liebknecht-Straße, where you can sit in the front seat of a Trabant; or else spend an afternoon at the former headquarters of the Stasi, East Germany's secret police, now an eerily fascinating museum.