U2 are mid-way through a four-night stand at Berlin today. They played the Mercedes-Benz Arena - in the shadow of one of the few preserved stretches of the Berlin Wall - on Thursday and Friday and conclude their visit to the German capital in the same venue on Monday and Tuesday.
Berlin is somewhere very close to U2's hearts, because it was here a quarter-century ago that they came to, in Bono's oft-quoted words, "dream it all up again". Decamping to a Berlin that was just emerging from the Cold War led to one of rock's great career reinventions and kick-started a creative burst that would result in Achtung Baby.
They got one of the last flights into the city before Germany was officially re-unified on October 3, 1990, and spent much of that harsh winter holed up at Hansa Studios, a couple of hundred metres away from the wall that had divided the city for 29 years.
I visited Hansa a couple of weeks ago in the company of Thilo Schmied, the founder of Berlin Music Tours, and got to stand in the spacious old ballroom where several of the songs that appeared on Achtung Baby, including 'One', first came to life.
Irish U2 fans heading to Berlin this weekend could do an awful lot worse than arranging a tour with Thilo, a music obsessive who grew up in the former East Berlin and was 16 when the wall came down. There's nothing about Achtung Baby that Thilo doesn't know, although he's just as comfortable shooting the breeze about Depeche Mode who have been regular users of Hansa over the years - two of their mid-80s albums, Black Celebration and Music for the Masses, were made there.
Of course, the reason U2, Depeche Mode and so many others including Snow Patrol and REM have been drawn to this studio and this city is because of the ground-breaking work David Bowie did there in the late 1970s. Low, "Heroes" and Lodger are cited as the so-called Berlin Trilogy, but "Heroes" was the only one that was entirely made at Hansa.
You stand in the ballroom and can almost see Bowie singing the title song with passion and King Crimson's Robert Fripp coaxing that soon-to-be famous riff from his guitar. Thilo brings me into the control room next door - where Brian Eno would have worked the mixing desk for both Bowie and U2 - and points out the window to where the Berlin Wall once stood.
It was at this very spot where Bowie famously saw two lovers "standing by the wall" and his imagination was fired up. In fact, the lovers were Tony Visconti, who was producing the album (with a little help from Eno), and a young German girl he was having an affair with. Visconti was married to singer Mary Hopkin at the time and confirmed the story of the origin of "Heroes" years later when his marriage had ended. Bowie knew full well who he was seeing but didn't come clean in order to protect his friend.
Bowie wasn't the only one to help put Berlin on the map in the late 70s. His friend and collaborator Iggy Pop made two brilliant albums at Hansa - The Idiot and Lust for Life - in an astonishingly fertile 12 months between the summers of 1976 and 1977.
The two were inseparable and lived in a pair of flats in a very modest looking apartment building on Hauptstrasse in the Schöneberg district. A trickle of Bowie fans pass here every day, stopping at the door of number 151, and taking the opportunity to have a drink in one Bowie and Iggy's favourite watering holes, the gay-friendly Neues Ufer, just a few metres down the street.
The importance of Berlin for Bowie was evident in 2013's elegiac comeback single, 'Where Are We Now?', which name-checked some of the places he used to hang out, such as KaDeWe, the city's most opulent department store, Potsdamer Platz, the public square that's been turned into a mini Manhattan much to the irritation of almost every Berliner, and the Dschungel on Nurnburger Strasse, which was once Berlin's answer to Studio 54, but no longer exists.
He doesn't mention SO36 in the song, but this scuzzy punk club, redolent of Lower Manhattan's now defunct CBGB, is still in business and was welcoming The Charlatans the week after I visited.
The appeal of Berlin to Bowie and Pop isn't difficult to understand when you consider the city's glorious early 20th history and the boundless creativity of the Weimar years before the Nazis came along and ruined everything (happily, Hansa survived a period of being used as a social club by the SS). And yet, the West Berlin of the 1970s was as permissive as the East was repressive and artists of all hues were welcomed with open arms.
The city continues to be a beacon for many musicians, including some from this country. Wallis Bird and Manu Le Tough have called Berlin home and Mick Flannery spent a year in the city, although he subsequently spoke of being weary of all the hipsters that populate areas like Kreuzberg. Those with an aversion to folks on fixed-wheel bicycles, and hipsterdom's other accoutrements, might want to look to another European capital - but they'd be missing out on a city that's managed to retain its artistic edge. There's value for money too: Irish bands wanting a change of scene would need a small fortune to relocate to the traditional London, whereas Berlin makes Dublin seem quite expensive.
My Berlin music tour with Thilo Schmied is almost over when he mentions that the city's reputation among musicians would likely have been far lesser had the famed 'Krautrock' producer Conny Plank accepted Bowie's invitation to work with him. Plank was based in Cologne.
Incidentally, U2 met with Plank in the mid-80s, in the hope that he would produce their next album (The Joshua Tree). But the German wasn't interested and his reason still raises smiles: "I cannot work with that singer."