I visited Danevirk and Hedeby on my way to the WHS of Jelling. There are several places where one can see the remains of the Danevirk (or Dannewerk in German), but the Viking Museum at Haithabu probably is the most worthwhile.

The Danevirk was the Viking's equivalent to Hadrian's Wall: built to keep out the barbarians. It covered a stretch of 30km in what is now the German state of Schleswig-Holstein (formerly in Denmark). Hedeby / Haithabu was the most important town in the region. It was located along the shortcut route between North Sea and Baltic Sea.

The Viking Museum at Haithabu has a modern presentation inside, though as so often there has not been found much of real interest from the Viking area. A lot of people seemed to have lost their money bag while getting on or off-board in the harbour!

The museum has a large outdoor part too. It holds a recreation of Haithabu in its original location, a part of the Dannewerk and the semicircular defensive walls of Haithabu itself. It's a great area for a longer hike: you can either walk on top of the Dannewerk, or do a full loop around the lake.