The nearest beaches are about 40 minutes away including Valras, Serignan and Gruisson plages. Narbonne Plage in particular has a beautiful beach of golden sand.
South of Perpignan are Argeles sur Mer and Collioure (about 1hr 30mins). These are extremely popular the former having a big beach but 50 camp sites around the town. Collioure is popular with artists.
The Costa Brava is about 2hrs 30 minutes away with a number of pretty small bays in the north away from the main tourist areas provides a sample of Catalonia.
Barcelona itself is only 3hours away.
Nearer to home Agde is an ancient city on the Herault river with three distinct coastal areas, Cap d’Agde a purpose built tourist area, Grau d’Agde a more traditional seaside area on the mouth of the Herault and across the river by ferry La Tamisserie which has a number of large camp sites.
For something different Sigean just south of Narbonne has an African themed safari park.