Visiting Vienna is a bit like someone landing an 800 pound Sachertorte on your head and inviting you to eat your way through it. It’s manageable for the first 10 minutes or so.
You may discover this when you first encounter the Hofburg, the sprawling Imperial Palace of the Habsburg dynasty. From humble beginnings as the seat of the Babenbergers, the place grew like a radiated ostrich, sprouting wings and libraries and stables and concert halls and crypts. To write its history here might crash the servers. Better to read all about it before visiting.
Emperor’s Bonus: 54 human hearts of the Habsburg rulers – including Ferdinand II, the crusader from Graz – are kept in the Hearts’ Crypt, behind the Loreto side chapel.