I guess that to get to Naantali is easy from Turku by bus, but as I drove there with my car, I am not sure exactly what kind or arrangement there is. Anyhow, it was only about 10 minutes drive from Turku.
Getting to Naantali is easy even without a car. There are frequent buses from the main square in Turku, and you can also go by the steam ship Ukkopekka in Turku, with the extra bonus of getting to see the archipelago.
As this town is by the sea it is very popular to have a boat here, either you have one or either you know someone who has one ;-)