In 2012, a Berlin art collective signed a 40-year peppercorn lease on a disused railway depot in suburban Berlin. Five years later, Centre for Art and Urbanism (ZK/U) has become a recognised hub of urban innovation and social activism. On the eve of ZK/U’s fifth birthday celebrations, Jana Perkovic chats to ZK/U co-founder and director Matthias Einhoff about ZK/U’s past, present and future.