The main airport is in Girona which is the destination for Easyjet, Ryanair and other low cost airlines. Girona can also be reach by train.
If you want to explore alot of the coastal cities then renting a car is your best option. There is regual bus service between the towns but nothing compares driving along and stopping where you like.
Girona - old city and jewish quarter, Cadaques marine park.
There are scuba diving outings to the "Islas Medas" National Reserve Park from L'Estartit. Cadaques also has various dive shops to explore the area.