"Are you going to the opening?"
Translation:Ska du gå på invigningen?
Yes, invigningen is one concrete occasion but att gå på bio or att gå på teater are general things, so those two denote an activity rather than a specific occasion. When you say 'the movies' in English, it's a bit of the same phenomenon. So gå på bio has a meaning that is more like 'go movie-watching'. If you want to say you're going to one specific movie theater you're more likely to use a demonstrative instead: Ska du gå på den bio(grafe)n? 'Are you going to that movie theater?'
It's when an artist has a private showing of an upcoming art exhibit before it officially opens, so to speak. Hence I'm a little hesitant to add "opening", since the opening technically comes later. But people nowadays often think that the vernissage is the opening, so the meanings are merging.