On the A8 from Bilbao, take the turnoff to the right marked "Islares". Turn right and park in the dirt parking lot. You'll see other vans there on weekends, mostly day surfers from Bilbao.
Once you've parked your car and suited up, walk straight toward the rock overhang where the break is. There are some stairs that lead into the water, jump off and the current will take you straight to the middle of the lineup.
Overview
Atmosphere
Good option when everywhere else is too messy/windy. Powerless, but fun.
General
Gets a little too crowded on weekends, considering the quality of the wave.