The original building was constructed in two stages over 25 years, beginning in 1866. The building was designed under the guidance of Colonial Architect James Barnet and composed primarily of local Sydney sandstone mined in Pyrmont.

The northern façade has been described as "the finest example of the Victorian Italian Renaissance Style in NSW" and stretches 114 metres along Martin Place, making it one of the largest sandstone buildings in Sydney.

Source: Wikipedia

Sydney GPO tower demolition in 1942

National Archives of Australia, 2017. Sydney GPO Tower Demolition in 1942. Retrieved here.