In cooperation with: andpartnersincrime, Staatstheater Kassel, why so empty. The seminar was supported by the Coordination Office for Service Learning and Community Involvement at the University of Kassel. Faced with the strained housing market and the climate crisis, andpartnersincrime, University of Kassel and Staatstheater Kassel are jointly taking aim at the social battlefield of vacancy and its political scope: In Kassel, at least 200.000 sqm are empty (gross floor area, equate to ca. 136 000 sqm usable area); They could be converted into approx. 2500 apartments of an average size of 55 square meters each. The studio researched and visualized this abundance of vacancies and developed designs for the reactivation and conversion of the former Postal Office in Untere Königsstraße, the Hansa Haus in Kurt Schumacher Straße and a state-owned villa in Goethestraße, currently all being vacant. In order to understand the cost of vacancies for the public sector, and the organizational, economic, and legal levers we have to counteract it, the studio furthermore developed public actions that visualized vacancies inside the city. The associated research studio LESS: Leere Stadt looked at underlying reasons for vacancies, examined constellations of actors, and researched which concepts can be instead applied for a public welfare-oriented urban development and against profit interests.