The historic center of Vienna is rich in architecture styles of the Austro-Hungarian Empire, including Baroque castles and gardens.
The so-called historical center of Vienna should be the old city of Vienna. The area within the ring road in Vienna should be regarded as the historical center, which includes the Hofburg Palace, St. Stephen's Church and other places of interest and historic interest.
Not sure this rates a separate entry, but be sure to explore the historic city centre. Whether it's crypts, museums or opera, you won't go wrong.
Walk through Vienna's World Heritage Old Town and experience history on every corner.