Within a time span of 10 years, the old colliery Zeche Zollverein in Essen, Germany, was transformed from a troubled brownfield to a celebrated UNESCO world heritage site. In 2010 it served as the central hub for events held during Essen’s year as European Cultural Capital. In this article I argue that we should consider Zollverein as an urban laboratory and understand its planning history as an experimental inquiry process in the Deweyan sense. I develop the concept of an ‘urban laboratory’ by paralleling the contexts of urban planning on Zollverein with recent developments in the philosophy of science and science studies on scientific laboratories. Laboratory work is understood as context‐bound experimental practice focused on resolving concrete problem situations. Theory and experimental practice are more closely linked than traditional views have held. Scientific inquiry must always be understood as a normative quest and cannot be reduced to a descriptive task of representing nature. Finally, I frame laboratory work as a transactive social process in which a community of inquiry is formed and transformed. These four ideas help to adapt the concept of scientific laboratory to urban planning contexts, and I use the Zollverein case study to illustrate these characteristics.