Nothing special in this fishing port. It's nice to visit the surroundings: Skien, Larvik and at least a detour by Oslo which is worth.
By air: Torp International airport is served by charters flights especially Ryanair. 110km from Oslo.
By rail: with NSB, links to all major cities (Oslo, Stavanger, Bergen, Kristiansand...)
By bus: with Nor-Way Bussekspress links to all major cities (Sandefjord-Oslo 1h45)
By boat: link from Sandefjord to Stromstad (Sweden).
By car: by road E18