not being an expert on the geography of Dublin, I was wondering which gaol is referred to in the song.

I am assuming that Brendan Behan wrote the song (although some say his brother wrote it) and I was intrigued to hear an introduction by the Clancy Brothers which stated that the song was about Kilmainham gaol, which overlooks the Royal Canal, but Behan never spent any time in Kilmainham gaol (he was only a year old when it was closed).

he did however spend time in Mountjoy gaol, so what I would like to know is whether Mountjoy gaol is in close proximity to the Royal Canal as well.