Possibly my favourite spot in all of Spain is the Cap de Creus (about two hours north of Barcelona by car). Windswept, jagged and wild, the area has some stunning coves with idyllic pebble beaches. Here's a tiny snippet I wrote about one of those beaches, the Platja de Sant Lluís, for The Guardian's on-line Travel section: Top Ten European Beaches by Foot. It's the same spot that I mention in The Sounder: Surrealism Meets Nudism. In the photo above, you can just glimpse the beach between the trees at the bottom of the cliff.
Even in August, when small boats are anchored off-shore, the beach is peaceful and the water absolutely sublime. Off season, when the crowds and pleasure boats of July and August disappear, it's even more delicious.
If you have time to ramble, the same path that leads you to Platja de Sant Lluís continues to the very point of the Cape, branching off to two other rocky coves along the way: the Cala Guillola and the Cala Jugadora.