Caerphilly County Borough Council’s five buildings on Tredomen Park in Ystrad Mynach were plunged into darkness to mark Earth Hour.
The annual event sees millions of people switching off the lights to their homes between 8.30pm and 9.30pm.
Earth Hour is organised by the charity WWF to show their support for a sustainable planet.
Famous landmarks across the globe took part on March 28 including The Eiffel Tower in Paris, Times Square in New York and Buckingham Palace in London.
The lights at Caerphilly Castle and the National Assembly of Wales were also switched off.