I would consider renting a car for a trip to see the lakes and water locks of Dalsland, and include a trip to the Norwegian city of Halden. Fredriksten Fortress in Halden is an interesting historic site.

https://en.wikipedia.org/wiki/Dalsland
https://en.wikipedia.org/wiki/Dalsland_Canal
https://en.wikipedia.org/wiki/Fredriksten