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.
Wrigthegaarden. See a concert at Wrigthegaarden. Many top Norwegian artists play here and there are even a few international acts as well. Elton John, Bob Dylan and B.B. King all played here. Also be sure to catch the monday jam-session where you will find talented locals as well as famous local artists such as Vidar Busk and Stephen Ackles pop in in every now and then.edit
Tangen Fort. Explore the Tangen Fort. A 30 minute walk south of the center of town through picturesque narrow streets with old white wooden buildings. edit
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.
Wrighteegaarden. Famous for concerts and lively summer crowd in the outdoor garden. Has an upstairs bar in the restaurant, a pub downstairs and a very nice seating area in the garden in the summer. edit
Tordenskiold. If you want to sing karaoke with drunk locals from the countryside this is the place to be. Head upstairs for trance/techno. edit