Stop by Halden Touristoffice for some useful tips before you start your adventure. It's an one-stop shop for travel information.
You'll have sightseeing choices galore when in Halden. Halden Touristoffice is a good place to begin here, but there are many other interesting spots to discover. Fredriksten Fortress, Vanninga, and Rød Herregård are close to the tourist information center and will round out your day nicely.