capital city and county in Norway
city and municipality in Østfold, Norway
urban area in Strömstad Municipality, Sweden
By train Halden is served by the Norwegian State Railway as the southern terminus of the Oslo-Halden line, which also continues to Gothenburg 3 times a day.
By Car When entering the country from Sweden, turn right just after the Svinesund Bridge, and follow the road signs to Halden.
By Boat You could take the boat from Sandefjord to Strømstad in Sweden. From there, you can take the bus, or drive by car. Estimate 30 minutes travel time from Strømstad.
If you own a boat of your own, sailing through the narrow Svinesund (a part of the border fjord Iddefjorden) brings you to Haldens beautiful guest harbour where you could stay for your visit.
By Bus You could take the bus from Oslo to Halden (and Strømstad in Sweden) http://www.nettbuss.no/ekspressbuss/timekspressen. Estimate 55 minutes travel time from Strømstad and 2 hours from Oslo.
More information available on Wikivoyage