The restored remains of the Rüsselsheim Fortress have become the new home of the city's municipal museum. The museum first opened in the 1970s and has now been completely rebuilt. A new staircase leads the visitors to the upper floor where they reach the main exhibition room. A newly added rooflight supplies ample daylight. We chose a limited number of different materials for this project. Next to the historic natural stone masonry we added an oak floor. Furthermore, we kept new structural elements in a simplistic white, while using dark gray painted steel for technical additions such as the elevator, doors and the main staircase. The architectural design makes the old house a perfect host for the new exhibition.