Sousse's Boujaffar Beach, with its multi-kilometre stretch of high-rise hotels, cafés and restaurants, is the city's landmark. Named somewhat incongruously after a local Muslim holy man, the soft, sandy strip is a playground where families picnic, children frolic, foreigners sunbathe and the warm, calm waters of the Mediterranean is everyone's bathtub.
Only a few small parts of the strip are claimed by beachfront hotels with chaise lounges and parasols. Though these are usually not roped off, they are 'protected' by staff that generally looks kindly on foreigners while tending to treat rudely any Tunisians who wander through. Access to these areas is generally open to non-hotel guests for a small sum however it's unlikely anyone will ask you for proof of residency. You'll find all sorts of water-sports equipment for hire along the beach. Don't leave valuables lying around unattended since petty theft is not unheard of.
In summer, the beachfront is packed with people sitting in the cooler evening air or strolling along the waterfront - a wonderful way to pass a summer's evening.