When first-time visitors arrive in the centre of Sydney, few expect to find the Cahill Expressway. It's the scar in the centre of the glittering city that many now believe shouldn't have been built. But when you look through Sydney's history books, things could've been a lot worse. Robert Freestone has tracked the design disasters Sydney avoided, in Unrealised Sydney. a new exhibition at the Museum of Sydney that charts the chequered history of redevelopment in the harbour city.