The 3rd prize in the competition for the new indoor swimming pool in Stuttgart-Zuffenhausen goes to 4a Architekten. The pool is designed as an open house that allows many views in and out, is clearly and functionally structured and designed for economic operation. To achieve this, the building mass was reduced to a minimum and translated into a compact design. In addition, the indoor swimming pool was developed as a plus-energy building. Solar energy and regenerative heat from the public sewer in combination with storage technologies are used as the main energy sources. The use of wood in the supporting structure and interior fittings ensures a good CO2 balance.