Thermoactive structures, seawater cooling and ventilation only as required: the Royal Danish Playhouse houses a large number of technical solutions, all of which contribute to lower energy bills and a sustainable profile. The location by the water has been exploited by using a heat pump to alternately cool down and heat up water from the harbor. The method means that the Royal Danish Playhouse can save between 75% and 80% of the energy required to cool the building. From using just sea water and the heat pump.