In 2007, the Barcelona City Council built a large underground electrical substation in the old town of the city, at Valldonzella Street. The three-level structure that hosts the substation is accessible from the street through a set of shafts and is blended into the urban environment.
The main volume of the building is shaped like a rectangular prism with the exception of one of the corners, which has added a volume with a triangular floor plan. The roof of the building sits 1.5 m below the street level. This allows the use of the area above it as public space, which has since become an iconic plaza.
The structural element used to retain the ground during construction was a diaphragm wall around the perimeter of the building, which also acted as a supporting structure for the floor slabs. These solid reinforced concrete slabs, which were cast in place, also rest on isolated supports. These supports were built as diaphragm wall modules, arranged in three principal directions to generate a main span length of 14.50 m.