A Greek firm has unveiled a hi-tech office block that relies on solar power for heating and cooling.
The mythical figure of Prometheus, giver of fire, adorns the building
The project, in a suburb of Athens, seeks to set an example in a country with a poor record in the use of renewable energy.
Co-designer Nikos Manioudakis claims the five-storey block is Europe's most energy-efficient building.
Greece enjoys bright sunshine for most of the year, but solar power is often used just for heating water.
Most energy consumption in Greek houses and apartments comes from air conditioning during the long, hot summers, the BBC's Malcolm Brabant reports from Athens.
In-wall and in-floor heating system
Underwater tanks help cool water
Building cooled to 18C in summer
The new Athens block captures the power of the sun and uses it primarily to cool down the building.
The block, in the seafront suburb of Palaio Faliro, is owned by solar energy company Sol Energy Hellas.
The building frontage has an image of Prometheus, the Titan of Greek mythology, who stole fire from the gods and gave it to man.
Water passes through a complicated network of pipes leading to underground tanks, where the constant natural temperature is 18C.
This cool water is used instead of air conditioning to make the building bearable during heatwaves.
"In the summer when we have an outside temperature of 35 or 40 degrees, we have an inside temperature of 18 degrees," said Mr Manioudakis.
"We hope we will set an example for other developers and designers, engineers," he said. "We're open for anyone who wishes to learn from this."
Greek power stations are among the dirtiest in Europe
In cold weather, hot water stored at the end of the summer is used to heat the block.
The building also generates some electricity, but it has to be connected to the national grid for lighting and to power the pumps.
The computer-controlled installations are 30% more expensive than standard heating and cooling equipment.
But the designers say savings in energy consumption mean the investment can be recouped within six years.
The designers hope that the "energy autonomous" building will make an important contribution to energy-saving research. Greek power stations are among the dirtiest in Europe, our correspondent says.
The Aristotle University of Thessaloniki and Greece's National Centre of Science Research have taken part the project.