I just have to choose Sirius Building by @betterthanhome as it's in my old neighbourhood of Sydney Harbour. I used to walk past it often and also see it out the window of my train as I looked down on the harbour. It is quite an ugly building (but lovable at the same time). It is a social housing complex, however most of the residents have now left. I guess people on social security no longer deserve million dollar harbour views according to the government. I believe the building is now on the market for developers to pull down and rebuild.
In keeping with the theme, I also like Abandoned by @dejan.vuckovic.