The Ruhrfestspiele is held each May and June and is one of Germany's most important theater festivals — unusual among major festivals for having a genuine working-class founding story. In the winter of 1947, miners from the Recklinghausen pits delivered emergency coal supplies to theaters in Hamburg; Hamburg's actors returned the favour by coming to perform for the miners. The festival has run every year since.
Today it draws international companies as well as German ensembles, and the programme covers everything from Shakespeare to contemporary performance and music. Tickets are reasonably priced by German theater standards. If you can time a visit to the Ruhr in late May or early June, the festival is worth building an itinerary around.