IT’S lunchtime in Siena, Italy, and the Piazza del Campo – renowned the world over for packing in the people at its spectacular Palio – is almost deserted.

A small group of students lounge near the famous fountain and a few pedestrians hurry across the square, but I seem to be the only one around who looks like a tourist.

Which might come as a bit of a shock to anyone who has seen pictures of this beautiful medieval city – a Unesco World Heritage Site no less – literally swarming with visitors.

But then it is early February and the “rivers of people” our guide tells us about mainly engulf the city from May to September.

It’s the same story at that other Tuscan tourist magnet 18 miles away, San Gimignano. And at the eerily silent hilltop fortress of Monteriggioni.

At nearby Colle di Val d’Elsa, famous for its lead crystal, the streets are ever so slightly busier.

But it’s so wonderfully quiet in Tuscany that I can barely believe I am in the same place that draws in 250 tour buses a day in peak season.

I can understand if you might want to go to Siena’s Palio – the most famous horse race in the world, where riders hurtle around the tight track in the town square. But at up to €700 a pop to cram on to one of the balconies (that’s if you can even get the chance), it’s a very expensive 78 seconds or so.

Much better, I think, to save your money and spend it on an off-season week in Siena and the nearby valley of the River Elsa, slowly savouring its delights, unhampered by the crowds.

So it seems almost a sacrilege to learn that most tourists who come to ‘do’ this part of northern Italy cram the ‘big three’ – Pisa, Florence and Siena, sometimes Lucca too – into three days. For, like the glorious honey cake that we tasted, Siena simply has to relished, morsel by morsel, from its fountains and courtyards, to its incredible works of art.

Wandering through its cobbled alleyways offers a tantalising glimpse of what, at times, seems a parallel universe. It may be a prosperous university city of upmarket businesses, restaurants and the most sumptuous five-star hotel in a former palazzo, but the underside reveals a proud and fascinating history and is a mirror to a hidden underground world.

Most of Siena’s riches are very obvious but, beneath the sandstone hills on which the city is built, lies its most precious commodity – water. Fonte Gaia (the fountain) in the Piazza del Campo is at the centre of a network of underground channels, called bottini, which run for more than 25km below Siena. They have been carrying water to the city since the 12th century.

There is currently an 18-month waiting list to tour the bottini, and that’s if the level of the water is not too high. Apparently the tunnels are filled with icons because their creators believed that going underground was going nearer to hell and the icons would protect them.

My disappointment at not being able to delve deeper – literally – into this city’s past was short-lived. This is a city which is said to still look much as it did in the Middle Ages.

This is where going off-season also wins hands down for me. There are so many treasures to see here that I couldn’t imagine waiting in endless queues to shuffle through Il Duomo (the 13th century cathedral), for instance, even though the magnificent floors with their tapestry of multi-coloured, etched marble would be on full view. Apart from August to October, the floors are kept under protective covers, but then Il Duomo becomes a peaceful museum, with its awesome Romanesque interior.

Neither could I imagine being packed in like a sardine among 30,000 other revellers in the Piazza del Campo for the Palio on a baking hot July or August day (it runs twice a year) with no toilets and only one way out of the square through a narrow gap.

Or, for that matter, trying to appreciate the breathtaking interior of the Santa Maria della Scala, opposite the cathedral, surrounded by hordes.

Like a great many sites in Siena this museum gives new meaning to the word ‘grand’, especially considering that it was a hospital until 1996. To be a patient here may have meant little, or no, privacy in a ward with 80 other people. But the sick and the weary pilgrims who came through the frescoed reception hall must have looked around them and thought they had arrived in Paradise.

Our only other fellow visitors were a group of nursery children, who were initially entranced into uncharacteristic silence before launching in to a ‘Where’s Wally’-like game to find the artist who had painted himself into each of the fabulous 15th century frescoes. These wall paintings by Domenico di Bartolo describe the mission and illustrate scenes from life in the hospital.

Our guide described the old hospital as “like a small town” and told how she loved to take the keys and explore when the director was not around. Indeed, explore you must in Siena. The Sienese are fiercely proud of their city, with a passionate allegiance to their contrada (districts). There are 17 contrada, with the boundaries marked with their symbol, whether it be a double-headed eagle, panther, caterpillar or a she-wolf.

San Gimignano’s ‘symbols’, of course, are its tall towers, particularly impressive from a distance. Wandering through the charming winding streets I tried to picture what this compact town must have looked like with 72 such towers rising above the medieval rooftops. There are ‘only’ 14 towers now, but they still lend a romantic fairytale ambience to the place.

San Gimignano has, quite rightly, been described as a ‘medieval treasure chest’, on which such renowned artists as Benozzo Gozzoli and Bartolo di Fredi have left their marks, a Duomo adorned with valuable frescoes and a fascinating archaeological museum.

But out of season you can really get to its heart and see the other treasures that tourists don’t usually get to see. There are free guided tours with art historians to places only open off-season and other treats, such as tastings of local products, including the wonderful Vernaccia wines.

Back in Siena, our guide – a very proud member of the she-wolf contrada – was reeling off another notable fact about the city. The world’s very first bank, the Monte dei Paschi di Siena, is here. Never having moved since the 14th century, it still has the papers from the day it first operated.

It is also a city very familiar to James Bond fans, with the latest movie Quantum of Solace filmed here. Daniel Craig stayed at the Grand Hotel Continental, the only five-star hotel in Siena which boasts a beautiful frescoed ballroom, restored by local artists.

When I asked our guide if Craig had been mobbed by fans, she looked quite shocked.

“We do not give too much attention to stars,” she sniffed.

Maybe that’s because the people of this part of Tuscany have far too many treasures of their own to take notice.