Just what will the massive 60-metre monument over Sydney’s main street be?

That remains clouded in secrecy until plans for a big unveiling on Tuesday at 10am. But an eagle-eyed smh.com.au reader appears to have spoilt the lord mayor’s surprise.

Hundreds of artists had expressed interest in the proposal and council had settled on a final design, which was wheeled out to those in the know weeks ago.

The council has voted to "recommend" the design, but refuses to say what it is until after it is formally adopted on Monday night.

But an smh.com.au reader has built a strong case behind Junya Ishigami, an award-winning Japanese architect who was known to have bid for the project. 

A fellow Japanese artist has listed on his resume that he worked as a translator for a project involving Mr Ishigami and City of Sydney council earlier this year. Mr Ishigami is also known to have visited Sydney around February.

SMH has confirmed with a source that our reader's hunch is on the money. Mr Ishigami’s firm has been contacted for comment. 

Identifying Mr Ishigami’s connection also offers further clues about the shape of the installation, which some councillors said had unnecessarily been kept secret.

Fairfax Media has already revealed that at its highest point the installation, described by sources as a "spiralling steel arch" is likely to soar above the Town Hall, which stands at 60 metres. It will probably stretch from the QVB to the Woolworths building, and stand diagonally across Sydney’s main street. 

Mr Ishigami, a critic in residence at Harvard University, was jointly awarded an architecture competition for Copenhagen Harbour last week. The design? A giant floating cloud.

That fits with interviews given by him, in which he expounds on his philosophy of "architecture as air" and says he pursues designs that "[float] lightly in the air, soft and fluffy like a cloud". 

The council has not yet responded to emails and it is unlikely to confirm the project before Tuesday morning.

But will that 60-metre spiralling arch be white and have the contours of a cloud? It seems likely.