This is a wall. It is also "The Wall".
The Wall is the most infamous gay pickup strip in Sydney. There are probably others - but this 100m of convinct built sandstone wall has a unique synergy. It runs along the eastern boundary of the old Darlinghurst Gaol commencing at the rear of the Supreme Court of NSW. Street prostitution is illegal in Sydney, whether it be same sex or mixed.
The wall (all four legs of it) was designed and constructed under the aegis of Francis Greenway from 1820 to 1822 but he, being a convict, was removed from the project, no matter his architectural gifts to the colony under Governor Macquarie. Convict markings can be seen in the sandstone blocks all along The Wall. They were used to ensure that each man did his fair share and did not slack off. Progress was painfully slow, however, in 1841, existing prisoners were marched from the original Sydney Gaol near the corner of George & Alfred Streets (the site of the current Four Seasons Hotel) to the partially erected Darlinghurst Gaol on a hill overlooking the colony from the SE.
So, what is the graffiti? It is not actually on The Wall but just around the corner in Burton Street. It is tempting to see it as man and boy - but that is my flight of fancy. And note that the graffiti is on concrete "implants". Maybe the man with the spray can valued the sandstone more than the government who contracted out repairs to this historic structure!