The dreary dome looks like a giant tortoise perched on the top of a hill in the countryside of northern France.

But beneath the enormous 50,000-ton structure is an underground Nazi complex that could have changed the world forever.

La Coupole, near Saint-Omer in the Pas-de-Calais region, was built to destroy London with V2 rockets.

With the capital within striking distance, it would have stored and launched 50 long-range missiles a day.

Terrifyingly, Britain came just a fortnight from this devastation becoming a reality.

Indestructible with 16ft-thick reinforced concrete, La Coupole survived a major Allied bombing campaign from March 1944 that badly damaged neighbouring villages. However, the site was abandoned in July 1944 after the Normandy landings – just two weeks before Hitler would have pushed the button.

The oldest rocket-launching pad in the world, La Coupole has just reopened to the public after a revamp and is only one of the historical scars on northern France – Nazi-occupied from 1940 to 1944. The region also saw the Battle of Agincourt, a major English victory against the French in 1415.

On a happier note, this year is the 490th anniversary of the meeting of Henry VIII and Francis I in the Field of the Cloth of Gold to improve Anglo-French relations.

Nowadays the two nations appear best of friends as I travel from Dover to Calais with P&O Ferries.

My previous cross-Channel dining experience of a soggy sandwich while surrounded by screaming schoolchildren is blown out of the water by Langan’s Brasserie, the on-board restaurant that I’m told is just as good as its famous Mayfair cousin.

Passengers can also avoid the crowds during the 90-minute crossing in Club Lounge, with a glass of champagne and other refreshments for just a few extra pounds.

The Pas-de-Calais region does not produce its own champagne – or wine, for that matter. But its Cote d’Opale coast is dotted with breweries, including Brasserie des 2 Caps, which uses hops from east Kent for some of its beers.

Perhaps the best example of French hospitality I found was Chez Tante Fauvette, a tiny restaurant near the Hotel Saint-Louis in Saint-Omer. It has a homely, intimate feel with stunningly simple food.

Owner Olivier Sowinsky plays the ultimate one-man-band as shopper, greeter, waiter and chef. I certainly don’t envy him the washing up!

Similarly delicious, but more modern, French dishes can be found at La Cour de Remi, in Bermicourt.

It is just a short hop to the site of the Battle of Agincourt, during which the French had at least double the number of troops as the English, but were overpowered by Henry V’s skilful arrowmen.

Our guide apparently has no shame in telling us that when the first line of the French army was defeated, two thirds of its other troops ran away.

If only the French were as good on the battlefield as in the kitchen, history would probably have been written rather differently.

For information on Pas-de-Calais, visit www.pas-de-calais.com.