Constructed immediately after the Central Library (on the left), between 1934 and 1938, the eight-storey extension was opened by George VI. It was built to accommodate growing administrative departments, but apparently includes an underground cinema.
Between the two ornate 'gable ends' (here's the other), the south wall of the extension is concavely curved around the circular Library; the dividing lane, Library Walk, is one of my favourite parts of Manchester.