Get on Kosterbåtarna, red/white ferrys that leaves just in front of Tourist Information Office in central Strömstad. Get off at "Kilesand, Sydkoster"
With ferry from Holland to Kristiansand, Norway. Then Drive 2.5 hours to Sandefjord where you go with the ferry Sandefjord-Strömstad. https://hollandnorwaylines.com