You have to take the A-8 motorway from Bilbao, going to Santander, the spot is very easy to find, cos as you leave Bilbao and it´s surroundings, you´ll arrive to a point where the motorway crosses a bridge and you´ll see an oil refinery in the left side and a beach break on the right side, just after crossing the bridge you´will have to exit the motorway and take a road that takes you to the beach, is very easy to find. No worries to get lost.
It must be said that there is a bit of pollution in the area because of the oil refinery nearby. The wave is very gentle and funny. You won´t have problems with locals if you don´t cause trouble.