If you want to arrive quickly by car the best option is to follow the E18 from east and if you arrive from west, you follow E39 to Kristiansand and then E18 from there to Grimstad. Grimstad is roughly midway between Oslo and Stavanger. Kristiansand is the largest city near Grimstad.
With modern express buses it is comfortable and easy to travel to and from Grimstad. There are numerous daily buses departing from Stavanger and Oslo heading for Sørlandet and Grimstad. The bus stop for express buses in Grimstad is called Øygårdsdalen and is located just off the E18. From the bus stop there is a 15 minutes walk to the town center and two minutes with taxi.
If you wish to take the train from east or west, there are several departures daily from Oslo and Stavanger. The nearest station is in Arendal and Kristiansand. From there it goes local bus to Grimstad with several daily departures.
Kristiansand Airport Kjevik is located 45 kilometers from Grimstad. You can arrive at Kjevik Airport by plane from major Norway cities. SAS, Widerøe and Norwegian have arrivals from Oslo, Bergen, Stavanger and Trondheim. There are direct international arrivals from Copenhagen, Amsterdam and Gdansk. You will find four car rental firms based at Kristiansand Airport Kjevik. From Kjevik Airport there is a shuttle bus going to Grimstad.
The coastal ferry routes to Southern Norway starts at Hirtshals in Denmark and ends in Kristiansand. The Color Line "Superspeed" ferry only takes three hours and 30 minutes. This route has two departures daily. In summer the Fjord Line ferry "Master Cat" takes 2 hours and 30 minutes. There are also several departures from Denmark to Langesund and Larvik.