I don’t think I’ll make it this year but if anyone else goes, please share your experiences. You’ll find the map to the places you’ll get entrance to here: http://english.openhousehelsinki.fi/map/3
/Edit 20/9/13: I found a very describing post about the visit to the Arabia porcelain factory as a part the Open House Helsinki.
Curious about a place that is normally closed for the public? 13-15. Sept 2013 is your chance to get a look at it! Last year I heard somebody had even gained access to the sewer system (don’t know if that is true but hey, who wants to see others shit?!)! See more about Open House Helsinki here.