David S.
Yelp
If you are a train lover then you can't beat the Adelaide Railway Station.
Actually, come to think of it you can because there is a train museum in Port Adelaide, and the trains simply come in, hang around for about 10 to 15 minutes, then leave so it isn't even all that good for train spotting (there are better places along North Terrace between the bridge and the research centre, that is if they haven't built over it by then).
Still, even if trains are not your thing, the building itself is quite impressive, and it is even listed on the heritage register. Even if you aren't catching a train anyway, you should at least walk across the concorse because the granduer of this 1920's building is outstanding. Hey, you don't even have to cross North Terrace because there is a tunnel underneath. While you're at it, you might even stop off for a coffee and one of the shops on the concourse and just watch people wandering past - who knows, you may even catch some people singing carols on the steps.