The City Circle is underground, in a loop entering at Central Station and running around Town Hall, Wynyard, becoming an EL at Circular Quay, then going underground again to St. James and Museum, and all of the main suburban lines in the city either run through the City Circle, or part of it. The Airport line also runs underground for four stations, including two suburban stations and the two airport stations (domestic and international terminals).

So while its mostly at ground level with the occasional dive or overpass, it is only the interurban and country trains terminating at Central that avoid going underground altogether.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.