Chateaux in the Loire are everywhere. Rich in history, architecture, cuisine, great wines and scenery, the Loire Valley is justly famous the world over. But there is much, much more. Underground.

What is not known is that here, around the chateaux and the Royal River as the French sometimes call the Loire, exist huge, silent, roofless worlds. Dug into the cliffs and slopes lie literally hundreds, possibly thousands of kilometers of underground quarries and caves, some of them large enough to drive into, others impossible to find, unknown, with entrances hidden or covered up, forgotten, never to be found again.

Mostly these worlds exist in pitch black darkness. Only here and there does light play with the mighty dark around an entrance or an opening from above. Or, yes, around a curtained window in the rocks. People live in them too. By the thousands. Troglodytic living has even become fashionable.

Visiting a vast, ancient quarry, a guide told me how to find my way out without a lamp, the way the rock miners of the past would do it should their oil lamps fail. Would I like to try? An interesting experiment! I said yes. My lamp was turned off, the guide left with it, knowing well where to find me.

Never, ever in my life had I experienced darkness like this. As soon as the guide's footsteps were no longer heard I was utterly and totally lost. I attempted to find my way by certain marks on the walls the way the guide had explained and which I thought I had understood. But obviously not.

Stumbling and fumbling, lost, I would have been in a state of total panic had I not known the guide would shortly come back to rescue me. I just sat down and saw the blackest blackness ever. And the silence seemed to roar.

As my anxiety diminished there was ample time for reflection. Right here, during the Cretacious period 100 million years ago there was an ocean where I sat. I imagined the huge ammonites, giant circular snails up to two metres in diameter crawling here, and big sharks and rays roaming the sea.

As the ocean's debris eventually settled over millions of years it turned into a thick layer of chalk-like rock here called tuffeau ¿ tufa in English. Easy to carve and dig into, tufa has provided shelter and refuge in troubled times for man as long as anyone knows.

There is a direct connection between the tufa and the magnificent chateaux, medieval fortresses, churches, cathedrals and even Roman walls of this region. Yellowish or whitish in colour, the tufa is easy to work, lightweight, and it hardens and becomes lighter, even white when exposed, thus an ideal construction material for monuments of beauty. The startlingly perfect chateaux of Samur, Chenonceau and Chambord were constructed with an especially fine, light and white tufa rock from Bourré.

Eventually, due to man's greed, underground galleries started to collapse, some right under villages. Now hundreds of kilometres of subterranean passages are abandoned although multiple uses still exist today for the outer parts of the tunnels and caves, ranging from a deluxe hotel to restaurants, night gardens, for growing mushrooms, champignons, art galleries and much more.

The most common use of all is for storing wine. With a steady temperature ranging from ten to 15 Centigrade depending on the cave, perfect humidity and darkness, the old quarries are ideal for aging wine. Hundreds of kilometers of wine cellars snake their way into the ancient stone. Les Caves Montmousseau in Montrichard have 15 kilometre of wine-lined galleries that may be visited every day throughout the year. Bubbly Saumur, fruity Vouvray, as well as Chinon, Sancerre and Bourgeuil have been bred to perfection here .

Based at the luxurious Le Domaine des Hautes Roches hotel in Rochecorbon, I visited some of the underground sites. The hotel itself is part of the troglodytic story.

Built into tufa stone cliffs, 12 totally different, spacious rooms have been created in old caves that were used and possibly dug out by monks of the Marmoutier Monastery around the year 700 BC. It should be mentioned that the cuisine at the Hautes Roches is superb.

For underground gastronomy, across the Loire from the Hautes Roches is another cave-riddled town by the name of Montlouis-sur-Loire. Hard to miss due to a huge sign on the main road, here is an immense troglodytic restaurant by the name of La Cave. With splendid high ceilings and a colourful interior it is a good place to experience the local cuisine. La Cave is one of several troglodytic restaurants, very touristy but spectacular.

Anyone who drives through this region with their eyes open will see troglodytism everywhere. Thousands of people are troglodytes, living completely within the stone. Doors and curtained windows, often with flowers, betray their presence. As do satellite dishes and chimneys higher up. Others have built a whole normal house front, but the back of the house digs into the rocks ¿ semi-troglodytic.

The galleries, the old quarries, are all privately owned so that you can see a façade of a house but, as guide Doriane Tardif told me: "When you see a house front you don't know whether it is six metres deep ¿ or a few kilometres."

"Live happily, live hidden," is an old saying in these parts.

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For more information on many other interesting troglodytic sites and activities, contact the local tourist offices of the region or: www.visaloire.com The site has an e-mail facility for further information requests. And note that the concierges of the region are usually excellent sources of information.

Except for the major chateaux that have very fixed hours, it is a good idea to call ahead for other sites. Roads and tourist sites are well marked The centre of just about every town also has a tourist information office. The basic tool is a good regional map where you can mark all the sites you want to visit.