The Playa de la Concha in San Sebastian is the best city beach in Spain, perhaps the whole of Europe. The sand is fine, the sea is clean and the city with all its great pinchos is right behind you.
There are actually three beaches in San Sebastian: this one (which is the most popular and famous), the Playa de Ondarreta (which is popular with families) and Playa de Gros, popular with young people.
Read more about San Sebastian in this San Sebastian Guide.
Next: Pictures of San Sebastian: Another View from Playa de la Concha