Arcachon has a direct train service from Bordeaux Saint-Jean station that takes around 50 minutes and runs frequently throughout the day. From Paris, the quickest route is a TGV to Bordeaux (about 2 hours) and then the regional train. There is no direct TGV service to Arcachon.
By road, Arcachon is 70 kilometres southwest of Bordeaux on the A660 motorway. The road can be very slow on summer weekends when half of Bordeaux is heading to the coast; arriving on a weekday or very early in the morning saves considerable time. A car is useful for reaching the Dune du Pilat and for exploring the bay's eastern shore, though the town centre is walkable and has a reasonable bus network.
The nearest airport is Bordeaux-Mérignac, about 60 kilometres away.