Dinner comes with a spectacle in La Tremblade. Before I sit down to a platter of oysters at La Cabane des Bons Vivants, one of the village’s canal-side restaurants, I stand and watch orange flames bellow up from a tangle of long, skinny pine needles inside a large, open oven. They are piled on top of a board of carefully arranged mussels and, by setting fire to the pine needles, the shellfish cook in their own juices.

This is the curious tradition of moules à l’éclade, a novel way of cooking mussels developed by Marennes-Oléron oyster farmers along the River Seudre in the Charente-Maritime, halfway down France’s west coast. The short-lived flaming spectacle is a prelude to sliding apart the charred shells and finding juicy orange molluscs inside – and just one highlight of our evening along La Grève. The avenue that cuts between the oyster beds, lined by colourful, ramshackle huts and rustic pontoons is an alluring venue for a sunset meal by the canal, the atmosphere all the more lively and fascinating for it being in a working oyster-farming village.

I’m with my family here in the Charente-Maritime, just north of where the Gironde estuary meets the Atlantic and around an hour south of the region’s more famous resorts of Île de Ré and La Rochelle. Our five days here will show us how a holiday rolls with the same alluring vibe as those settings farther north, but costs less and has more to explore (our base is a comfortable villa in the village of Étaules), with towns such as Royan on the itinerary.

The first stop for any self-catering stay in France, though, is the market. Royan’s is out of this world. Completed in 1956, the Marché Central de Royan has a decidedly futuristic vibe; inside, the 50-metre-span dome is lit by a space-age pattern of skylights, suggesting this flying saucer might take off at any moment.

Its offerings are equally impressive, and we stock up on cheeses, including a creamy Brillat-Savarin and a fruity Comté; charcuterie, including the local terrine, le grillon charentais, and saucisson; a big blousy lettuce, crunchy cucumber and a perfumed melon. It takes some resistance to say “C’est tout, merci” when each stallholder says “Avec ceci?” (What else would you like?) after each choice, and we come away laden with bags of fresh, local goodies.

A short walk from the market is another mid-century marvel, the Église Notre-Dame de Royan. Like the market hall and much of the local housing, it was built as the town recovered from Allied bombing towards the end of the second world war and is extraordinary – especially when you catch sight of its concrete belltower and sharp angular structure above the roof-lines. Inside, it is even more impressive and is said to have provided inspiration for the audience hall in Dragonstone in the TV series Game of Thrones.

A triangular stained-glass window is framed by V-shaped pillars that tower above, punctuated by thin windows of white glass. We explore its balconies and hidden features between the concrete alcoves, before coming outside into the bright sunlight. The beach is a few steps away, but we resolve to return, when our gastronomic treasures aren’t wilting in the car.

When it comes to beaches here, we’re spoiled by choice. The children have brought bodyboards, so we head to Plage Le Vieux Phare for action on the Atlantic waves. It’s overlooked by a cartoon-like red-and-white painted lighthouse, the Phare de la Coubre. A queue is snaking from its entrance and the views from the top are said to be wonderful, but we choose to enjoy it from the beach instead – what with it being 35C.

We hike across the soft sand to the life-guarded area a short distance from the ruined old stone lighthouse. Soon we’re jumping and riding the ferocious waves and the sight of the beach, east and west, disappears in a haze of sea spray.

The beach we visit the next day is more sedate; a day trip to the Île d’Oléron takes us to Plage de Boyardville at the north of the island. Our drive takes us through pine forests and deep woods that expand across the island, which is twice the breadth of the Île de Ré. We park beneath towering pine trees and follow the path to the beach, a picnic of our market spoils in the cool bag. The boardwalk leads to a perfect crescent and a shallow lagoon in which children tumble and splash.

To my left, the silhouette of Fort Boyard looms on the horizon. The concept behind this architectural curiosity dates from the mid-17th century but it was finally completed amid tensions between the French and English in 1857. The fort was intended to guard the coast but soon became obsolete and was used as a prison. From the beach it looks quite small, but distances can be deceptive: it is in fact 68 metres long and could house 250 soldiers with 74 cannons. Recounting my hazy memories of the 1990s Fort Boyard TV game show – a kind of Crystal Maze at sea only with tigers and Dirty Den (Leslie Grantham) – warrants a raised eyebrow from my 12-year-old son.

After indulging in ice-cream sundaes at Le Café de la Plage, we head into Saint-Pierre-d’Oléron, the island’s main town. It’s late afternoon on a Sunday, so few shops are open but there’s a four-piece jazz group playing on the main street, which brings an upbeat lilt to the sleepy town. With hollyhocks swaying in the breeze, white-washed, green and grey-shuttered houses, and long early evening shadows, it is reminiscent of the Île de Ré, only a little scruffier, which adds to its charm. We browse the shops that are open and wander back to the car, feeling sleepy and sun-kissed.

As we drive over the bridge back to the mainland, the tide has come in under it, and several aluminium oyster-catching boats are speeding by beneath.

The village of Mornac-sur-Seudre to the south is also reminiscent of the Île de Ré, with its white-washed houses, creeping wisteria and bright pink oleander bushes. We go early evening for a sundowner, next to its own waterway and oyster beds, and see more moules à l’éclade going up in flames outside the seafood restaurant Le Parc des Graves. We window-shop the gift shops and galleries, annoyed we didn’t get there earlier.

La Tremblade is our favourite though, and so we return to La Grève for a final meal at La Cabane de la Grand-Mère, which does its mussels differently – moules à la brasero. The recipe, borrowed from oyster-farming communities near the Mediterranean, sees them marinated with herbs, onions, white wine and olive oil and then cooked on a griddle over a fire. After swigging back a platter of briny oysters, we tuck into the steaming pots of mussels and agree these are the best we’ve ever eaten. I ask the owner how they are cooked and she tells me the recipe. “All the very best flavours!” she laughs. When I say how they’re even better than moules à l’éclade, she smiles and says: “Ah but, with the éclade, it’s a much bigger spectacle! The flames are amazing!” I can’t disagree.

Transport from Portsmouth to Caen was provided by Brittany Ferries; return crossing from £224 for a car and a family of four. For more information on the area, see infiniment-charentes.com

• Carolyn Boyd is the author of Amuse Bouche: How to Eat Your Way Around France (Profile, £10.99). To support the Guardian, order your copy at guardianbookshop.com