“The Box” is a conversion of a former warehouse which was built in 1969 and had finally an interim usage as a venue. Because of the special location of the building with a view to the river and the already existing flexible building structure which could provide space for different work environments, a (re-)usage as an office building was an obvious solution. One aim of the conversion was to keep the existing prefabricated concrete skeleton construction including the stiffening staircase cores and to integrate them into the new spatial and structural concept. This existing skeleton construction has a curtain wall of exposed aggregated concrete panels. The square floor plans have a measurement of about 36,8m. We decided not to tear down the building with its gross floor area of approximately 7500m² but to preserve its unique industrial charm. To keep and emphasize the conciseness of the building volume it gets a circumferential maintenance walkway consisting of expanded metal.