The city loop, or 'the loop' refers to the train stations
Flinders Street,
Melbourne Central (formally known as Museum),
Parliament,
Spencer Street and
Flagstaff on
Melbourne's railway system. Coupled with the tram system we have here in Melbourne, travelling around the city is fairly easy.
Melbourne Central,
Flagstaff and
Parliament stations are all underground, but look
imho rather nice.
I'm also pleased to note that it's fun watching people's mobile phone conversations cutting out while going on the underground segment of the loop.
Disclaimer: I have not travelled on other railway systems so I am not really able to objectively compare the efficacy of Melbourne's train system.