Sandefjord is a great place to check out small inlets, farms, and hills that attribute to Norway's great scenery. The view from Mølleråsen Hill are quite good. Situated just north of the town it gives you a great panoramic vantage point to look at the fjord surrounding hills, and farms. The rocks are great to just sit up on maybe even for a picnic. There is also a bench set up there. It can get quite windy though.
The one thing that made Sandefjord a big town is its whaling industry. The city has a little whaling museum which presents the history off whaling. Inside you can see various objects like boats, paintings and harpoons and such.
This restored ship, the Southern Actor, a mid sized whale ship, lies in the harbour of Sandefjord during summer and you can visit it then.