The old office building at Groot Willemsplein, Rotterdam, dating back to the 1940’s, was renovated to give it a new life with commercial functions on the ground floor and flexible office spaces at the other floors. The most important climate adaptation and mitigation measure implemented is the energy-efficient cooling and heating system. An Aquifer Thermal Energy Storage (ATES) system supplies the building with heat and cold. In summer, heat will be absorbed and stored in a ground water aquifer, this stored heat can be used in winter to heat the building. During the summer period cold water from another part of the aquifer is pumped up to cool the building. In this way the infrastructure is associated with climate adaptation (being prepared for increased cooling needs in summer in a sustainable way) and mitigation (reduced emissions of carbon dioxide). The additional heat that is needed comes from district heating (excess heat from nearby industry). The rooftop garden is a further implemented adaptation measure dampening the effect of more frequent heavy showers; in addition it is an attractive recreational green space with special attention for birds, bats and insects.