|Bothwell Street in Balaclava (via Augustus Brown)|
This is a common way these things get started - looking on a map and noticing lines that look like they could be railway lines. Much like with the evolution of animals, sometimes what is still present today bears the hallmarks of being built around something that is no longer there. It is just a launching point, you need to back it up with more research - but there's no doubt that it's the kind of thing worth paying attention to, and you get a feel for how these things look when you've been doing this for a while. The good thing about railway lines is that they don't do sharp corners, which makes it easier to join the dots.
Augustus tweeted about it, appealing for information, and @EnsignR replied with a link to the Wikipedia page for the St Kilda and Brighton Railway Company, which had rails in that general area - but said they weren't on VRhistory.com's maps, which are usually a go-to source. I looked and it turned out they were on the 1860 map (which isn't linked to with the rest), but they went a different way; they would reverse from St Kilda Station and go in kind of a loop, before joining the extant Sandringham line just before Windsor Railway Station (then "Chapel Street").
|Inner Melbourne in 1860 (via VRHistory) & Windsor today (via OpenStreetMap)|
All of that meant that the line on Bothwell St probably wasn't the St Kilda & Brighton RC line. But nonetheless, @colinfry666 found old maps from 1866 and 1900 that show what appears to be a railway line there (first going through parkland, then with Bothwell St around it). So what was it?
|Maps of the area in 1866 and 1900 (via @colinfry666)|
According to the website, the place where the school and the St Kilda Town Hall now stand used to be the site of the St Kilda Markets. Markets, stockyards, quarries and factories are all good candidates for a lost goods siding, so this too was suggestive.
At this point in the investigation, the provisional verdict was: Yes, there was a line down Bothwell St as Augustus suspected. No, it didn't connect to St Kilda Station (though we found another lost railway that did). It was probably just a short goods siding for produce/livestock/whatever to get to the St Kilda Markets which stood in that triangle.
This is where it gets a bit more difficult, because we've taken the low-hanging fruit but have not yet come to definitive conclusions. So to confirm our suspicions we would have to do some more serious research, which can take a lot of time and effort (more than I am willing to spend on a line I'm not particularly interested in). This could mean sifting through a lot of old books and maps that often aren't available online; it could mean visiting the site in person to see if there are any clues that you can't see from satellite imagery or Street View; and at the end of the day the answer you're looking for might not even be there - it could have been lost to the sands of time altogether.
But alas, as often happens, it turns out we'd misinterpreted something. There wasn't a railway line at all - the lines on the original maps were for a drain/pipeline. It still exists today, it's just underground. Colin found a more complete version of the 1866 survey which showed this, and he discovered where the open-air part of the drain is still visible today, just north of the Town Hall.
|The full 1866 survey, and the junction today (via @colinfry666)|