Langesund is a small coastal town in Telemark.
Bus from Kristandsand and Oslo stop on the highway which is a ten minute drive from Langesund.
There is a direct bus from Skien, Porsgrunn and Stathelle. From Porsgrunn you can take train to Oslo or Notodden.
Langesund is a quite small town compared to seatowns in southern Europe. Getting around is by that, obviously not a big problem. You can easily walk trough the whole city, from the Bamble city hall in the north to the bay in the south. The city involves plenty of small streets of northern standard which is difficuld to drive in with a car. Walking is the best solution.
Langesund is a town full of life in the summer season with live music every evening, many restaurants, small streets with shops, fishermen, smell of fish and seawater.
Walking to Tangen Fort is a good alternative if you want to learn about history from the German occupation. Make sure to read something in beforehand, or involve a guide to your trip. There are also signs along the way with information.