Travelling to Royan presents several options.
By car from the UK you can take one of the long Channel crossings and then travel down the west coast of France via Nantes and La Rochelle or you can cross at Dover and use the motorway network via Rouen and Tours. A third, if rather long, option is to take the P&O ferry to Santander in northern Spain and then drive up through southwest France to Royan.
Travelling by air you have the choice of La Rochelle airport (no flights from the UK during the winter) or Bordeaux airport. By car from La Rochelle to Royan is about an hour and from Bordeaux is about an hour and a half. Alternatively there are direct trains to Royan from Paris although it is worth checking if it is faster to go by TGV to a nearby main city such as Poitier or La Rochelle and change to a local train.
Once you are there a car is really useful if you want to explore the area around Royan particularly inland. However there is a very useful regular bus service (CaraBus) radiating out from the railway station that covers most of Royan, the coast and the Arvert penisula.
Useful links:
Royan Bus Service
French Rail Network
Out & About