David,
We went to Spain last year and stayed at a site called Playa Joyel, this is in the town of Noja and is about 42km (30 miles)from Santander.
The site has a Pool complex, but no waterslides and you have to wear a swimming cap (males and females), it has direct access to the beach, which is sandy and has a good surf for bodyboarding.
The town itself is not too comercialised and has the usual Bars and Restaurants plus Shops, but be aware the locals speak limited English (as opposed to the Med).
We are planning on going back next year, just pricing the ferries at this moment in time,
best regards, Martin