Together with Barceloneta beach, these are the city's oldest and most traditional beaches. They were the first to have amenities for bathing, an activity that was the exclusive domain of the city's well-to-do classes at the time. The recent building of a hotel has created a small, peaceful cove where you'll find a number of restaurants.
http://www.barcelonaturisme.com/wv3/en/page/1113/sant-sebastia-beach.html