A passport of stamps. Come within a hundred metres of a place and it stamps itself, or press the button on the place screen. The stamps make a poster: your route on parchment over the outline of the 1989 Wall, the places numbered in the order you reached them, ready to share. Then and now. Thirty places carry an archive photograph beside the modern one, each with its year. Hold the picture and it fades to the other. Full screen, a handle wipes between them. Listen. Every place is read aloud in English by one recorded narrator. Twenty five of them run about ninety seconds, written for the ear rather than the page. Nothing plays until you press play. Berlin transport, explained. What U, S, M, RE and F mean on the signs, what the zones are, and where a ticket is sold, online and at machines in the city. East and West are now filled in on the map from the first launch, without going into the filters.

The city that is gone. Fifteen buildings that no longer stand, each with a photograph of what was there and the year it came down: the Berliner Stadtschloss, the Palast der Republik built on its cleared site, the Anhalter Bahnhof, the Sportpalast, the Ahornblatt, four of Berlin's lost long-distance stations, and the border crossing at Bornholmer Strasse that opened first on 9 November 1989. Where the Wall stood, from Berlin's own 1989 survey of the front wall, not a path near it. East and West. The two halves of the divided city as map fills, and a line saying which side you are standing on. Eight walks. The Cold War, Prussian Berlin, Berlin in one day, Kreuzberg, Prenzlauer Berg, Charlottenburg, the vanished city, and one with children. Every walk follows real streets, numbers its stops on the map, and remembers where you stopped. Icons on every row of the map filters, so the list can be read by shape. Five places were in the data twice and are now in it once.