DH loves Scandi-noir (the Killing/ The Bridge etc). He and I are both widely travelled but never proper northern Europe. DS2 suggested Denmark/Sweden this summer instead of a villa on the Med <sob>. Probably 10 days.
So, ferry and drive? 'Ryanair'? Multi-centre holiday? Camp?
We have always camped, and enjoyed Denmark pre Noir- been 4 times. But there are chalets to hire on camp grounds and hotels of course!
Driving in Denmark is easy peasy, but getting there may be a pain as the direct ferry has stopped, so involves a drive up from Netherlands/France.
Our fav places are Skagen, Aarhus, Copenhagen, Aero, Bornholm but there are many many many more which we visit on the way to places.
Lots of free/cheap history- viking graves etc- would recommend Aalborg, the ship at Ladby, Roskilde. Castles and design galore. Beaches are cool too. In Copenhagen it is worth getting the Copenhagen card, we did a 3 days card spread out over 4 by using half days. Also visit Sagnlandet Lejre and if you can, any of the 'bog' people such as Tollund man or at Silkeborg.
Easy to get across to Sweden from Copenhagen (we didn't enjoy Sweden as much ) but there's lots to do.