La Grande Motte (30 minutes away) is well-developed and a favourite of Parisiens. Busy but huge beaches so plenty of room and plenty of activities including tubing and windsurfing with showers on beach. You’d be advised to book activities in advance.
L’Espiguette (30 – 45 minutes away depending on traffic) is a wild beach with no facilities but paid parking. Popular, especially with kite surfers, but huge. L’Espiguette is just along from Grau du Roi, which has a bizarrely good aquarium. Lots of horse-riding available at L’Espiguette, including trekking along the beach.