New building complex at the Karlsplatz in the centre of Stuttgart. Mixed-use for offices (ministries of the State of Baden-Württemberg), apartments, retail outlets and restaurants as well as a three-level underground carpark in the basement. The main construction is designed as a reinforced concrete frame structure with bracing cores. The frame allows for maximum design flexibility, also for future development. The floor spans of between 6 to 10 m could be realised economically using 30 cm thick flat slabs. In some areas with longer spans the slabs are prestressed. The recess of the upper floors could be realised by inclined columns. The three levels below ground are executed as a "White Tank" (watertight concrete Basement) against water pressure. The foundation is designed as an optimised slab foundation. The project is located in a mineral water protected area. To make a third level below ground possible, the water protection layer in the soil was included in the 3D-model of the building.