There’s no getting away from it – I have a romantic imagination. The sight of a fortified village or castle on a hill really fires me up – curiosity goes into overdrive and I want to know who, what, why and when. Nor is it simply castles: I love the way the landscape changes as we drive along in the motorhome.

On this trip we’ve enjoyed the scented air of pines and eucalyptus along the coast, viewed crops and cattle on the plains, vineyards climbing the hills, and ancient olive groves rambling around rocky limestone crags. Driving west, approaching the Spanish border on the way to Evora Monte, the forests give way to a land of dry grass, olive trees and other rocks, surprisingly like millstone grit. (Millstone grit? Think Ilkley Moor and Brontë country.) For miles these outcrops kept appearing beside the road – great, dark, rounded shapes, looking exactly like stranded hippos.

Our site, Camping Alentejo, is also on the high serras (sierras in Spanish) but here the landscape is different. Surrounded by vineyards, olive groves and cork plantations, we’re also close to huge marble quarries and the beautiful town of Estremoz, where the marble is as fine as that from Carrera. Everything there is marble, even the kerbs and the cobbles – as is the palace of Vila Viçosa, once home of Catherine of Braganza, wife of Charles II…

But that’s another story. The one I want to tell you concerns the humble wine cork.

Arriving at the campsite, I took a photo of one of the cork oaks, glowing like fire in the evening light. Info from reception told us that a cork factory is nearby, where the owner welcomes visitors. We all know about cork mats and tiles, but in Portuguese shops Anne and I had seen products from hats to shoes, wallets, handbags, and even umbrellas. How were they made? And what about that little cork in the bottle of wine?

Capt Peter and I have been fascinated by the cork oaks ever since our first trip through Portugal some years ago, so along we went next day with Anne & Fred to find out more.

A charming young man showed us around the cork factory, explaining the process from trees growing in the yard to the stacks of bark awaiting treatment. The trees are specially pruned to encourage large branches, and must be 23 years old before the first cutting is made. After that, nine years elapse between each harvest – the bark being carefully removed by hand. Then it is boiled and pressed flat, ready for use.

These oaks can be 250-400 years old, so precious that none can be cut down without government permission. As the tree gets older, the cork becomes thinner and finer; but it seems that only in its earlier life is the bark the right depth and density for wine corks, and only 4% of the harvest makes the best ones for the finest wines.

Our guide told us that the seven grades of cork are assessed by experts, with prices varying from 85 euros to 700 euros for just 70 kilos of bark. And despite the diverse products appearing in local shops – don’t let’s mention the plastic bungs – we were surprised to hear that real wine corks are where the money is made.

Inside the factory we saw the wine-cork-making principle – a cutter is simply driven down through the bark. Today it’s automated, but we were shown a century-old machine, rather like a lathe, which made just one cork at a time. (They must have needed an awful lot of machines and operators in those days.)

What about the waste – the bits of unused cork? Well, it’s minced and mixed with glue to make things like tiles and insulation. I bet you didn’t know that cork is used to insulate nuclear submarines – and even the nose-cones of spacecraft. (Although I imagine a somewhat thicker density than the tiles on your bathroom floor.)

The very old cork oaks, whose bark is thin and finely-textured, donate their bark to the shoes, handbags, wallets and umbrellas. It’s finely shaved and backed by a thin holding material – and remains flexible and washable for years.

But as to cork’s primary purpose, after sampling an amazing bottle of local Borba wine at lunch, we toddled along next day to a nearby adega – winery – and bought a few bottles to take home. All with proper corks, of course. And would you believe, even the label was made of cork…