This article presents the fundamental points of the accomplished work regarding the energy upgrading of the building of the Natural History Museum of Crete, Greece, based on a cluster of passive and active measures. The main target was the building's energy efficiency upgrading from D to A+ rank. Among the passive measures, insulation of the building's envelope, installation of new windows and doors, construction of a green roof and planting of an outdoor space at the south side of the building to improve the ambient climate locally are included. Furthermore, small wind turbines and a photovoltaic station on the roof, geothermal heat pumps with an open loop system operating with seawater, new lighting equipment controlled by a central management system and reactive power coefficient compensation constitute the proposed active systems. Energy saving percentages from 40% to 93% are achieved with all the proposed technologies. In total, the primary energy specific consumption is reduced from 273.65 kWh/m(2) at 18.36 kWh/m(2), giving a total energy saving percentage of 93.29%. The building's energy efficiency is upgraded from the rank D to the rank A+, according to the European Union's standards. The total cost of the proposed measures is estimated approximately at 900,000. (C) 2017 Elsevier Ltd. All rights reserved.