La Marsa has a long sandy beach running the full length of the corniche — easily two kilometres of beach right in front of the cafés. The sand is clean, the slope is gentle, and the water is shallow enough for children well out from shore. In summer it gets very busy, especially at weekends, but you can usually find a spot.
Further north along the coast, the beach at Gammarth is quieter and is where the top-end hotels are concentrated. Both beaches are free to use. There are no lifeguards. Beach cafés sell drinks, snacks, and rent sun beds and umbrellas at modest prices.