Kelenföld Power Station is an abandoned power plant control room in Hungary. Built in the 1920s, it's a beautiful example of Art Deco industrial architecture and features a dramatic oval-shaped room lit by a large skylight. The plant originally ran on coal but was converted to natural gas in the 1970s. Much of the original control equipment remains intact on the green metal wall panels. A concrete bunker housed an air raid shelter during World War 2, underscoring the control room's role in a critical infrastructure at a turbulent time.
Designed by two prominent Hungarian architects, site is protected under Hungarian law and so cannot be demolished. This does mean it also can't be restored and maintenance is difficult. It is occasionally open to tours and also film shoots, apparently.
More info & photos
4 huge housing estates with "commie blocks" get heating from here, and a lot of older parts of Buda was retrofitted with district heating in the 70s. I couldn't find exact numbers, but around 1-200000 people live in these parts of the city.