A hush falls over the moonlit courtyard. The rhythmic percussion of countless cicadas is replaced by the sweet pulsations of a dozen violins, their melody winding up into the hot Italian night like clouds of perfumed incense. Where harsh German voices once barked orders and dusty boots shuffled and stamped, tonight there is only the serene mystery that is music, its soothing balm consigning fear to distant, painful memory.

And what music. Those Nazi officers who drove into the sunlit quad at the heart of the Tuscan edifice of La Foce would have been appalled to know it would later resound to their notion of degenerate art. There is a sense of quiet triumph in listening to Schoenberg's Transfigured Nightin this setting – such an elegant repudiation of a grotesque, twisted ideology.

When Hitler's dirty and dishevelled troops arrived at Anglo-American writer and scholar Iris Origo's vast Val d'Orcia estate in 1944 they were already on the run, desperate and dangerous, being forced up through Italy by the Allies' slow and costly advance. With partisans in the woods above the house and Canadians and Scots Guards inching towards them, La Foce found itself caught in the middle. Children evacuated from Turin were sheltering in the cellars and escaped prisoners-of-war hiding in the attics; they were extremely dangerous times, bravely recorded with clarity and honesty by Origo in her famous diary, War in the Val d'Orcia.

When the fighting became intense, and La Foce looked as if it might be directly in the crossfire, Origo felt she had no choice but to move the frightened and distressed children. With all transport requisitioned and no petrol anyway, they simply walked all day across the battlefield, shells falling all around them, to the hilltop town of Montepulciano, hiding amid the crops and ditches to avoid menacing aircraft and columns of German troops. Somehow, this extraordinary party of 28 children, four babies and some 20 adults made it to safety, with the people of Montepulciano coming out to greet them with open arms.

Music in the courtyard at La Foce.

The drama of those war years and Iris's own, sometimes tragic, life was captured last year in the first performance of a new piece based on her writings, The Land to Life Again, which brought to a close the annual festival of music staged at La Foce – just one of many classic festivals across the country that can make a visit to already special Italy even more rewarding for keen music-lovers.

The young Italian composer and conductor Francesco Cilluffo wrote the song cycle while staying on the estate and was clearly inspired by the beauty and history around him and by the quality of Origo's writing. "I wanted to get the feel of the landscape in the music," he told me. "I wanted to try to describe how the rhythm of life was cruelly interrupted, and yet out of all that destruction and hurt came a message of deep humanity and renewal."

The piece, given its premiere by the soprano Nuccia Focile and young players from the UCLA Camarades, tells of Origo's struggles to regenerate the estate's exhausted farmland in the 1930s, her desire to establish her now famous garden, the privations of war and the personal tragedy of losing a son to meningitis – a passage written as a duet for voice and cello, poignantly played on this occasion by her grandson, the cellist Antonio Lysy, who also runs the festival.

He has great vision for music in this wildly beautiful region (south of Siena and west of Chiusi) and told me he wants one day to stage an opera based on the war diary at the Teatro Policiano in Montepulciano, where Origo finally managed to house the children safely after their dangerous march. With a starry list of patrons including Vladimir Ashkenazy, Charles Dutoit, Hans Werner Henze and Maurizio Pollini, his ambitions might be realised, and not only in music. Hollywood has expressed interest in the diary, too. That could explain Colin Firth's name among the patrons.

Francesco Cilluffo returns this year when the Incontri in Terra di Siena, to give it its full title, will be celebrating its 25th anniversary. He'll be conducting Wagner's Siegfried Idyll in a festival that features the cellist Ralph Kirshbaum, the pianist Andrew von Oeyen and the extrovert Baroque quartet Red Priest. Music from Bach and Vivaldi to Verdi and Piazzolla will be heard in the buildings and gardens of the estate and in the castles and churches of the Val d'Orcia from 19 to 28 July.

When Antonio and Iris Origo bought the estate in 1924 they found a beautiful but derelict landscape peopled by illiterate peasants living in great poverty. They set about building new farmhouses, a school for the children and a clinic and social club, now an attractive restaurant called Dopolavoro.

Today, one of the 1930s farmhouses is a small hotel. La Bandita lies above La Foce, up what is probably one of Italy's most famous roads, reproduced on millions of postcards and on thousands of calendars. It winds in S-bends up a hillside, cypress trees standing sentinel at its side, a perfect depiction of all things Tuscan. It looks idyllic, but in truth it's merciless.

Imagine driving over a rocky beach to get to your hotel and you have some idea of the condition of the road. It was made by Antonio and his men from great boulders and chunks of stone and took me 45 minutes to negotiate the three miles in my faithful VW. It's a serious impediment to anyone wanting to tour the region. Once you arrive, a little shaken, you are rewarded with a spectacular view of the Val d'Orcia, its mysterious treeless landscape unforgiving in the hot summer sun or the snows of winter. And the prices are equally unforgiving. A room for the night costs €295-€395 in high season: the pigsty suite, €495-€595. The impoverished farmers of the 1930s would surely gasp in disbelief.

Essentials

For more information on the Incontri in Terra di Siena, go toitslafoce.org. La Foce is 60km south of Siena. Perugia airport is the nearest airport, with Ryanair offering flights from £20 one way (ryanair.com). Pisa airport is two hours away by car. EasyJet (easyjet.com) flies to Pisa from £46.78 one way.