In 1980, German architect Oswald Mathias Ungers (1926–2007) participated in a competition for solar housing. His contribution received a special prize, but the design was never realised and has been largely ignored since. Yet it remains the only project in which the architect explicitly addressed the issue of sustainability. This publication brings his design to light once again, and is the outcome of an unconventional approach to the architect’s design practice that was undertaken as part of the 2018 summer school at the Ungers Archiv für Architekturwissenschaft (UAA) in Cologne. What can the position of an “outsider” contribute to the debate on sustainability?