The great Reformation painter, Cranach the Elder, spent his final year here in 1553. Minding where I walked and keeping an eye out for crumbling masonry, I found myself in Isherwood's world: the old tenements known as Mietskasernen with their endless dark courtyards, peeling plaster and abandoned bicycles. I turned off the newly redecorated streets, with their clean pavements, smart restaurants and new Turkish-run Imbiss (snack bar cafes). Prenzlauer Berg, which escaped a lot of the bombing and is now undergoing a facelift, still contains good examples of top-heavy balconied facades and dirty plaster frontages.

The Wall made it a backwater shared by Turks and punks on the one side, the post-'68 Alternative scene on the other. Today, with the Wall down and the Oberbaumbrucke across the Spree re-opened, it is fast becoming a central part of Berlin again.I made for the former eastern sector. The KDW department store, Berlin's answer to Harrods, outside which Isherwood describes the elderly prostitutes, moved to West Berlin. The site is occupied by the Checkpoint Charlie Museum.A reversal of circumstances has also occurred in Kreuzburg, the working- class area where Herr Issyvoo lodges with the Nowaks. In Isherwood's time, the fashionable area was already the Kurfurstendam and West Berlin. Zoo Station still serves all destinations west, but Lehrter Station, under construction in the centre of the new Potsdamer Platz, will centralise the capital's railway network.

Slowly, and complicated by land-ownership claims, re-building began. It now boasts a brand-new Galeries Lafayette and many smart shops and is set to be the trendy street it was before the First World War. For decades it was a sort of no-man's land, with Checkpoint Charlie astride it and the only underground station linking East and West Berlin beneath it. Turks run the markets, the bakeries, the clothing shops and the fast-food outlets. They have filled the commercial niche that was occupied pre-war by poor Jews. Next door, the rebuilt synagogue has become a museum.But replace Isherwood's Jews with present-day Turks and you have a very credible remake of his Berlin. They are generally well accepted in West Berlin and have, as the Jews did, established a lively cultural scene, even if their spread into former East Berlin has created tensions.As for the setting, Friedrichstrasse is back in the picture, though it has gained in associations.