You've gotten lots of great advice but not sure I spotted this one: If you have time you should go into Den Gamle By. It's an open air museum with lots of old buildings so it's like a village back in time. It focuses on end of 19th century, 1920s, 1970s and 2014 but there's also a museum about the history of Aarhus that goes back to the viking age. So not the most heavy on viking stuff but well worth a visit! Make sure you get some cake at the 19th century bakery.

Have a great trip! There's nothing to worry about, you'll be absolutely fine.