San Sebastian has fantastic beaches adjoining the city centre. It's a great city for food, not just at the Michelin starred restaurants. Cheaper restaurants offer fixed-price menus del dia, much cheaper at lunchtime than at night. Cafe Oquendo does an excellent three-course lunch, inc 1/2 bottle wine for €16pp. So fill up at a leisurely lunch, sleep it off on the beautiful Playa de Concho till 8 o'clock (Spanish style) then shower/change & hit the many excellent pintxos (tapas) bars in the adjoining old city (Parte Vieja).
C/Oquendo 8.
Tel +34 943 420 736, cafeoquendo@terra.es.
Google map: tinyurl.com/34eg9h9