Cudillero is well communicated by road, train, planes, bikes and on foot.
By car, just take the A8 direction until you reach the sign for Cudillero (VIAMICHALIN), or maybe catch the bus (ALSA), or combine the train routes (Renfe) or (Feve), or if you are doing the Camino de Santiago Coastal route on foot or by bike just follow the shell until El Pito and then on to Cudillero. Oh! nearly forgot, and you can fly into the local airport (Asturias), just 12 Kms away, catch a taxi or if the timetable is conveinient, walk an hour to Felgeras and catch the bus which comes every hour, I did this not so long ago, there's a great bar there.
There are lots of interesting ways to travel to Cudillero, I've tried them all. I'm going to gradually add more routes to this site and the blog dedicated to moving around Cudillero and getting to.