Hi Jeremy,
Not sure if you are only planning the northern coast of Spain... but here are some locations that I know. Before that, watch the tides, as Vieri said, some beaches are dangerous, since they are under cliffs and when the tide comes in, and comes quickly, you can see yourself trapped away the exit point, that maybe to reach it, you have to go swimming if you are not careful. This is specially relevant in Catedrales Beach, in my home region, if you are in the right part of the beach (looking at the sea), the exit is on your left, and to get out, you have to pass for a point that the tide will be higher. You will not be the first person that has to go with your camera bar over your head...
The list is the places that I know, but not an expert in that coast, so probably I'm missing a lot.
Close to Bilbao:- San Juan de Gaztelugatxe: you can park here:
https://www.google.es/maps/place/43%C2%B026'33.9%22N+2%C2%B046'19.4%22W/@43.4427601,-2.7808027,7227m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4427613!4d-2.7720481 , then walk until here
https://www.google.es/maps/place/43%C2%B026'42.8%22N+2%C2%B047'02.6%22W/@43.4452171,-2.7928027,7227m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4452175!4d-2.7840478 . In theory this a more direct way, but they told me they are doing some construction work on it so you don't have access. Some examples:
https://500px.com/search?submit=Enviar&q=san+juan+de+gaztelugatxe&type=photos The main problem of San Juan de Gaztelugatxe it that it was used in the last season of Game of Thrones to represent Dragon Stone Island, a friend of my that lives close by told me that now it is always full of people visiting the place for just that reason.
To get down... you will need the tide to low, and be careful, the rocks are very slippery.
- Sopelana:
https://www.google.es/maps/place/43%C2%B023'25.3%22N+2%C2%B059'27.8%22W/@43.3903522,-2.9998217,7234m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.3903527!4d-2.9910668 , very easy beach to access with some possibilities:
https://500px.com/search?q=sopelana&type=photos&sort=relevance- Barrika:
https://www.google.es/maps/place/43%C2%B024'20.1%22N+2%C2%B058'20.0%22W/@43.4055691,-2.9809807,7232m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4055699!4d-2.9722256 This is one of the most famous beaches in Spain to do photography... and surf... but the beach disappears in hide tide.
https://500px.com/search?q=barrika&type=photos&sort=relevanceCosta Quebrada (Cantabria)- Arnía -
https://www.google.es/maps/place/43%C2%B028'20.6%22N+3%C2%B055'02.4%22W/@43.4723981,-3.9260917,7224m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4723991!4d-3.9173375 <-- Park there, don't go down the slope with the car, it is quite easy to get your car stuck and it is just 1 minute walk. This is a very good place for sunrise picture. If the tide is half low you can go down the beach, if it is high, I will recommend to see over it. Here stars a walk path:
https://www.google.es/maps/place/43%C2%B028'18.2%22N+3%C2%B055'11.5%22W/@43.4717151,-3.9286057,7224m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4717158!4d-3.9198515 that take you over it. you can do nice pictures over the top area:
http://dgpfotografia.com/tag/arnia/- Urros -
https://www.google.es/maps/place/43%C2%B028'20.6%22N+3%C2%B055'29.6%22W/@43.4723771,-3.9336527,7224m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4723778!4d-3.9248976 , if you continue walking to the left (looking to the see) from Arnía high view, you will reach the Urros area.
https://500px.com/search?q=urros&type=photos&sort=relevance- Somocuevas:
https://www.google.es/maps/place/43%C2%B028'08.0%22N+3%C2%B056'32.7%22W/@43.4688741,-3.9511817,7224m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4688747!4d-3.9424266 The tide needs to be low to get nice pictures in the right side of the beach:
https://500px.com/photo/224226419/into-the-light-by-ram%C3%B3n-m-covelo?ctx_page=1&from=search&ctx_q=somocuevas&ctx_type=photos&ctx_sort=relevance - Pedruquios:
https://www.google.es/maps/place/43%C2%B027'48.3%22N+3%C2%B056'49.2%22W/@43.4634101,-3.9557547,7225m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4634114!4d-3.9469996 -
https://500px.com/search?q=pedruquios&type=photos&sort=relevance- Valdearenas and Canallave beaches:
https://www.google.es/maps/place/43%C2%B026'57.4%22N+3%C2%B057'49.0%22W/@43.4492741,-3.9723717,7227m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d43.4492751!4d-3.9636167 . One of my fauvourite beadches, specailly the right side, Canallave.
http://dgpfotografia.com/tag/valdearenas/ By the way, in summer all that area is going to be full of people, lot of people from Madrid go there for summer time. So make your hotel reservations with time.
Best regards,
David