What is up to 60 metres tall and runs through the centre of Sydney? The City of Sydney council will not say.

Exactly what plans lord mayor Clover Moore and her colleagues at the council have been looking at has been a closely held secret. But intriguing details are now leaking out.

Cr Mandla threatened to go public about the proposal on Monday and so inspired debate about how democratic decisions about public art can or should be reached.

''I was told the public rarely likes public art but they grow fond of it over time,'' Cr Mandla said of a discussion with a council official.