He calls himself Bill, though it goes without saying that it's not his real name. And he doesn't want any photos taken of his face. He is, after all, a left-wing extremist.
We are standing next to Kottbusser Tor metro station in Berlin's Kreuzberg district, in a trash-strewn square in the shadow of an elevated section of the subway. If things go as Bill and the rest of the German capital expects, stones and bottles will be flying here in a few days' time as part of the city's annual May 1 protests.
Bill is wearing cargo pants and a T-shirt bearing the slogan "Die Yuppie Scum." The T-shirt is the sign the tour group were told to look out for at the arranged meeting-point underneath the railway tracks. Two dozen people are waiting for him.
Bill says they'll set off in a moment -- after he's collected their money.
Bill is a left-wing extremist who came up with a money-making scheme. He offers tours of the sites of "the famous May Day riots", sometimes in English, sometimes in German. Bill is American, so he finds the English tours easier to give. They also attract more people.
He hands out flyers advertising "revolutionary Berlin" and featuring a picture of Berlin's iconic television tower and a communist red star. The tour even has its own website and Facebook page.
Today's tour includes visitors from New Zealand, Ireland, Russia, and Italy. Their ages range from early 20s to early 30s. Many of them have recently moved to Berlin. They wear brightly-colored scarves and large sunglasses, but just for reasons of fashion, not to conceal their identity. None of them object to being photographed. The May 1 protests in Kreuzberg are simply another exciting aspect of their adopted home that they would like to find out more about.
It seems like the riots are the highlight of spring in Berlin. There are posters up everywhere, and the newspapers write about it on a daily basis. There are also quite a lot of Germans on the tour.
Bill says he usually charges €5 ($6.60) per person, but is willing to be flexible. He says he donates the money to a left-wing project, and that the tour itself is free of charge. After all, Bill is a Marxist, in other words an anti-capitalist.
Bill came to Berlin as a student eight years ago. He was in Kreuzberg for his first May Day protest seven years ago, and he's been coming back ever since. The day after last year's protest, his parents called. They said they'd seen a report about Kreuzberg on the news, and were worried about him. This is the anecdote Bill kicks off his tour with.
By the time we get to the Oranienplatz square, Bill has finished expounding about the background to the May 1 protests: squatters, the student movement, and student leader Rudi Dutschke, whose attempted assassination sparked riots in Berlin in 1968. Passing the offices of veteran Green Party politician Hans-Christian Ströbele, who was one of the lawyers that defended Germany's far-left Red Army Faction terrorists in court in the 1970s, Bills rails against him. Ströbele, he complains, is just like everyone else in Kreuzberg: not half as radical as he used to be.