I cannot resist chestnuts. Soon they will appear in the shops again, and, like the sailor’s wife mentioned in Macbeth, I’ll sit with a bowl in my lap and munch and munch and munch. Mostly, our chestnuts come from France and Spain, and fine nuts they are too – but a couple of years ago, I had a revelation in a fancy butcher’s in southwest London.

On the counter stood a basket of chestnuts the size of new potatoes. They were marrone from Monte Amiata, in southwest Tuscany, one of a handful of places that apply an AOC to their chestnuts. The growers and councils of the region are so proud of their tradition, they have laid out a network of paths through the groves and called it La Strada della Castagna, the Chestnut Road. As I set off with the intention of walking along it, my thin excuse for gluttony was transformed into a healthy autumn break.

Monte Amiata is an old volcano, and its worn cone, wooded to the summit, is visible from far and wide across the provinces of Siena and Grosseto. The Etruscans held the mountain to be sacred and, at Bagni San Filippo, the water gushes hot and sulphurous from the hillside. The outdoor swimming pool at the spa hotel where I was staying is heated at a constant 40C and has the power to dissolve baked-on stress.

I met Giorgio Gianneschi in the small village of Santa Caterina. He was a member of the team responsible for the Chestnut Road. For more than a millennium, the culture of chestnuts has been the defining characteristic of Monte Amiata. The trees thrive above 1,500ft and below 3,000ft, forming a band around the mountain, the castanetum, comprised of fruit-bearing groves lower down and wilder woods above. “Chestnuts were all the people had to eat,” Giorgio said. “The flour made from them was the staple food of the poor. You can understand why, when some prosperity came to the region, people stopped eating chestnuts. Some old people on the mountain simply cannot touch them any more.”

The path below Santa Caterina, following a rough cart track, illustrated what had happened to many of Amiata’s chestnut groves, abandoned to nature’s care. The mature, fruit-bearing trees still stood as orderly markers, but, in between, a jungle of young, wild trees and brambles had sprung up.

In contrast, the path that starts at Tepolini, halfway between Castel del Piano and Seggiano, passes through some of Amiata’s finest and most cared-for chestnut groves. It begins at the lower edge of the castanetum, where vines and olives merge into enclosures of stately old chestnut trees, looking more like a park than a working landscape. Its keepers were moving slowly under the trees, bent double as they filled their baskets. When the rain came, we took shelter in a stone hut with a man called Franco and his demijohn of country wine.

Franco’s trees had been in his family for ever. He pointed to the nearest, a senior servant that had been grafted by his great-great-grandfather. There was a ring of scar tissue near the base of the trunk, where the fruit wood had been joined to the rootstock. All the varieties of Amiata – and Giorgio estimated there are about 300 – were propagated in this way. This tree was a marron, but plant one of its nuts and the resulting offspring would revert to the “wild” rootstock.

Three hundred varieties? It was a conservative estimate, Giorgio said. Franco grew three types, and, as the rain eased, we ventured out for a lesson in chestnut identification. Franco gathered up a selection of nuts representing the two types of marron he grew, the buono and the cecio. After he had talked me through the striations, the colour, the size of the base, the fuzziness of the apex, I began to see the difference. The nuts were huge, but there are even bigger varieties. Under another tree lay the proof – the rossolina. In a good year, there are only 35 of these nuts to the kilo, while marrons average 60, but what makes the marron the more valuable lies inside.

The kernel of the rossolina is divided in two, and the inner membrane is difficult to remove. The marron has a thicker membrane that comes away more easily, and the kernel is free from fissures and divisions – an ideal nut for candying.

EVERY WEEKEND in October, there is a festival somewhere in Amiata, and there were three during my stay. In Abbadia San Salvatore, the medieval lanes of the old town were decked with chestnut boughs and littered with nutshells. Chestnuts were being roasted on every corner, either in wire-mesh drums like tombola cages or in vast iron pans, and the strolling crowds shucked and munched them incessantly. Every town lays on communal lunches and dinners, volunteers serving up to 200 people at each sitting. Outsiders are welcome, so Rossano Rossi, the owner of Il Castagno, a restaurant in Vivo d’Orcia, took me to dinner in the town’s Casa del Popolo.

Vivo’s festival is a celebration of chestnuts and mushrooms, of which the porcino takes pride of place. Crostini topped with mushroom pâté and chopped porcini in oil were followed by polenta ai funghi and rolled pork with chestnuts and roasted mushrooms. I felt oven-ready myself by that stage, but there was more – castagnaccio, a flat pastry made with chestnut flour, raisins, pine nuts, olive oil and rosemary; monte bianco, a sweetened paste of boiled chestnuts topped with whipped cream; and, finally, a much-needed digestif, chestnut grappa. This gourmet repast was served without pretension, on plastic plates. Rossano introduced me to another Giorgio and his wife, Mariella, both retired, who offered to take me next morning to look for mushrooms.

At last, the sun came out. The woods were tinged with russet, and the road out of Abbadia soon climbed into their shade. These were the wild chestnut woods where the trees were tall and straight and close-growing. All around, falling chestnuts knocked against branches and trunks. We could have filled sacks with them, but we failed to find any mushrooms.

We moved farther up to the beech woods before striking off uphill, where the ground showed signs of wild boar. Giorgio found several small porcini, but I was beginning to despair of contributing to our haul when I almost trod on a fine specimen, 10in tall. It was the best mushroom we found, and was duly admired by Elizabeth, the proprietor of the Albergo Generale Cantore, where we repaired for lunch.

The albergo stands 1,000ft below the summit, a convenient stopping place, but whether I could ever start again after Elizabeth’s Sunday lunch was in doubt. The mushrooms were whisked away to the kitchen, and arrived four courses later as accompaniment to lamb chops. The meal ended, after two more courses, with pecorino and chestnut-blossom honey. I spent the rest of the week trying to walk it off, but to no avail. Everywhere were new opportunities for chestnut-stuffing that I was powerless to resist.

Travel brief

Festivals: the main chestnut festivals this year are: Bagnolo and Castel del Piano, October 5-7; Monticello Amiata (14); Roccalbegna (13, 14); Abbadia San Salvatore (13, 14, 20, 21); Vivo d’Orcia (14, 20, 21); Arcidosso (19-21, 26-28); Santa Fiora (27, 28); Campiglia d’Orcia (28); and Piancastagnaio (November 1-4). For further details, contact the local tourist office (00 39 0577 775811, www.amiataturismo.it).

Getting there: Monte Amiata is 80 miles from Florence and Perugia. Fly to Florence with Meridiana (0845 355 5588, www.meridiana.it), from Gatwick, or to Perugia with Ryanair (0871 246 0000, www.ryanair.com), from Stansted. Rome, 130 miles away, is served by British Airways (0870 950 8950, www.ba.com), EasyJet (www.easyjet.com) and Ryanair.

Getting around: a car is essential on the mountain, as public transport is infrequent. A week’s rental starts at £115 with Opodo (0871 277 0090, www.opodo.co.uk) or Auto Europe (00800 223 55555, www.autoeurope.com).

Where to stay: in Monte Amiata, try the Albergo Generale Cantore (00 39 0577 789789; doubles £52). Also recommended are Terme San Filippo, in Bagni San Filippo (0577 872982, www.termesanfilippo.it; doubles from £67); Cortevecchia, in Semproniano (0564 984075, www.agriturismocortevecchia.it; doubles from £52); and Agriturismo Le Case, in Castiglione d’Orcia (0577 888983, www.agriturismolecase.com; doubles from £49).

Where to eat: a three-course meal in Monte Amiata will set you back £15-£20. Further afield, try Il Castagno, in Vivo d’Orcia (0577 873831); Antica Fattoria del Grottaione, in Montenero d’Orcia (0564 954020); and La Tana dell’Orso, in Castell’Azzara (0564 951547).

Tour operators: Monte Amiata is on few itineraries, but Activity Breaks (028 9039 5705, www.activitybreaks.com) offers three-night spa packages from £175, excluding flights. A local operator, I Viaggi di Re Ratchis (00 39 0577 775200, www.toscanasegreta.it), offers bespoke itineraries. Italian Dreams (029 2035 0100, www.italiandreamstravel.co.uk) hopes to offer summer walking and wine tours from 2008.