‘Here there are wild boars with four legs, and wild boars with two,” says Walk Italy tour leader Roberto Carpano. We are drinking volcanic wine in the tiny village of Sovana, and he is referring to the fact that people from this forested, hilly part of southern Tuscany (50 miles south of Siena and as close to Rome as Florence) are sometimes nicknamed cinghiali (wild boars) for their stubborn, bristly nature.

Not that there are many locals about – Sovana has fewer than 100 residents, and the piazza is deserted apart from a small, self-important dog. My partner and I are here, with four others, to join a two-day walking tour of the area’s mysterious vie cave (sunken roads).

We are not exactly off the beaten track, for these tracks have been beaten since the bronze age. The vie cave are a network of paths dug by the Etruscans, the civilisation that ruled this area until 100 BC, when the last of their cities were absorbed into the Roman Republic. The ancient thoroughfares were cut into the tufo – the volcanic rock common in south and central Italy – connecting settlements, religious sites and necropolises. Some are just sunken footpaths, but others are six-metre deep ravines broad enough to drive a chariot down. In places the walls are carved with sacred symbols to protect against the pagan spirits later populations believed might haunt the trails.

Facebook Twitter Pinterest High society … Pitigliano is an ‘unreal vision of a town’ . Photograph: Shaiith/Getty Images

Our journey begins above Sorano, at Fortezza Orsini, the 15th-century castle of the Orsini family, perched atop a tufo bluff riddled with tunnels and caves. We tour the catacombs with Sean Lawson, a New Zealander who came here on holiday 18 years ago and stayed on. He leads us through the cramped passageways that honeycomb the rock – their walls coated in saltpetre, used for gunpowder that fuelled the Orsinis’ incessant wars – and into the wooded valley, where the vie cave begin.

The sunlight disappears as we burrow into the shaded valley – the marks of 2,000-year-old picks are still visible on the walls. But soon we emerge into an open landscape of vineyards and olive groves, roads more Roman than Etruscan. Our goal, eight miles to the east, is a place of even greater mystery: an ancient necropolis called the Città del Tufo, whose largest, most majestic tomb is the Ildebranda, carved from the living rock, surrounded by hundreds of smaller burial chambers. Sean shows us the Tomb of the Winged Demons and a statue of Vanth, angel of death, pausing to chat to some local women who are picking wild asparagus – it’s perfect in risotto, they say.

The next morning’s vie cave take us south from Sovana to a place that’s very much alive: the Sassotondo vineyard, owned by wine producing couple Carla Benini and Eduardo Ventimiglia. “He is the mind and I am the nose,” says Carla, after showing us round a cellar cut deep into tufo, like everything else, and pouring glasses of red, white and orange wine as an icy wind shakes the mimosa trees outside.

Facebook Twitter Pinterest The wine cellars at Sassotondo vineyard are cut deep into tufo

After a lunch of unsalted Tuscan bread and sheep’s cheese sprinkled with oregano, we are back on the sunken roads heading for Pitigliano – an unreal vision of a town with steeples, towers and defensive walls on a rocky outcrop, its terracotta rooftops circled by rooks. We pass beneath the arches of a 16th-century aqueduct into a warren of vicoli, narrow twisting alleyways. Roberto shows us the synagogue of the ancient Jewish quarter, which thrived from the 15th century but didn’t survive the 20th – its members fled or were deported, with others reportedly finding refuge with Christian families during the second world war – and is now another monument to a vanished culture.

A full moon is rising as we settle into La Magica Torre, a guesthouse with views of the old town. Sleep is a long way off, though, for something special is about to happen in the main piazza. The Invernacciu is an effigy of canes and straw, which represents the departing spirit of winter. As darkness falls, a line of flames weaves towards us along the vie cave across the valley. A procession of young men in monks’ robes staggers up the hill, trailing sparks from huge bundles of burning canes on their shoulders. Their chants get louder as they come: “’Eppe, ’eppe, viva San Giuseppe!” This festival, the Torciata di San Giuseppe, is dedicated to the town’s patron saint, but the veneer of Christianity is unconvincing. Tonight is the spring equinox, and this is a pagan celebration of the end of winter.

The monks touch their torches to the pyre and the straw man goes up in flames. A fierce wind turns the piazza into a maelstrom of swarming sparks. Chunks of burning wood rain down on the crowd, and parents brush embers from their children’s hair as watching firemen chat and smoke cigarettes. As music blasts from powerful speakers, inebriated monks dance hand-in-hand around the inferno.

It is a glorious end to our walk. Winter is truly over. By midnight the streets are deserted. We return to the smouldering heap to gather a handful of still-warm ashes to take home on tomorrow’s train – good luck for the coming year.

• The trip was provided by Walk Italy Tours, whose six-day guided tour of southern Tuscany costs from €599pp, including half-board accommodation (self-guided option from €399). Train travel from Paris to Milan was provided by Thello, which has sleeper tickets from £25 for a six-berth cabin, and from Milan to Capalbio (an hour’s drive from Sorano) by Trenitalia