The crowds outside the Uffizi are not much shorter out of season. Book a VIP ticket in advance and you stand in a queue to collect it then stand in line to surrender it and by the time you've done all that you may as well have queued up with everyone else. Today, though, I have Roberto Martelli at my side. Dapper, bearded and speaking English come Americano, Roberto is a native of Florence and slips me inside in record time. That is what he is paid for, that and his knowledge of Botticelli, Leonardo and Michelangelo.
I get a lightning tour of the Renaissance, as we elbow our way through crowds gaping at Primavera, The Adoration or the Tondo. Then it is time for my appointment, because before flying out I took advantage of a new cultural package offered by Abercrombie and Kent. At 11am a very tall, anonymous wooden door is opened on the top floor of the Uffizi. If you've passed it, you'd have assumed it led to the intendente's office or the place where they keep the remaindered postcards. But no, once Roberto and I are admitted we find ourselves in a silent other world. Steep stone steps covered in rich carpet lead down to the Vasari Corridor. The Medicis walked it on a daily basis; Hitler visited it in 1938 and Marc Chagall came here when he was made an honorary citizen of Florence in 1984.
The Corridoio Vasariano leads from the Uffizi in the centre of Florence, over the top of the Ponte Vecchio and into the Pitti Palace. It is a tall and gracious private passageway connecting where Cosimo the Great lived and the city state he governed. Built in just five months, the Vasari (named after its architect) was intended to allow the Medicis to get into the office without having to mix with the murderous plebs below. In 1565 the plebs weren't at all happy with Cosimo, who'd grown tired of just being Florence's banker. He wanted to be Duke of Tuscany, too, and, once duke, he didn't want to be assassinated. To get his patron safely into work each day Vasari built a sealed corridor from one side of the Arno to the other. He did it in record time, bulldozing through existing buildings when he could and skirting them when he had to. That it happened so quickly is extraordinary, that it looks so beautiful is beyond belief.
You cannot just walk into the Vasari Corridor. You have to apply at least a month in advance and be accompanied all the way by someone like Michele, our security guy, who is there to make sure I don't damage or steal any of the pictures. This is the other remarkable thing about the Vasari Corridor. In the 19th century, when there were no more Medicis left to assassinate, the corridor was turned into an overspill art gallery for the Uffizi.
As we reach the bottom of the steps, Roberto shows me scorched paintings that were hanging when the terrorist bomb of 1993 went off below, killing five people, demolishing the Quisisana Hotel (where A Room with a View was shot) and wrecking these canvases.
We then turn the corner and come face to face (literally) with more than 700 self-portraits. This is what the Corridoio Vasariano is famous for these days. The Medici collected artists' self-portraits, everything from Tintoretto to Van Eyck to Vige le Brun, one of France's first women painters. When the collection passed to the state in 1865, the corridor, hitherto just a thoroughfare, became a superb gallery of the self-portrait.
As we pass over the tops of shops on the Ponte Vecchio, Roberto draws my attention to "Cosimo's Eyes", round barred windows that allowed the paranoid duke to spy on his subjects. In the middle of the bridge, however, there are large picture windows that look west down the Arno to the three bridges that were rebuilt after the Wehrmacht withdrew in 1944. The Ponte Vecchio and the Vasari would have been blown up too to impede the Allied advance, but Hitler sent word that it was not to be touched. He had fond memories of these nine windows installed on Mussolini's orders to allow the Fhrer a good view when he visited Florence in 1938.
As we leave the bridge itself we pass a window that was cut into the outer wall of the 14th-century Santa Felicita church when the Corridor demolished its portico, thereby affording the Medici a view of divine service. Roberto and I then followed a dog-leg diversion round the outside of the Mannelli Tower. In 1565 the bolshy owner refused to allow the corridor to pass through his property, so Vasari simply diverted it round the outside like a car going round a cliff edge on just one set of wheels.
At the gallery's end we find a wedding portrait of the last of the Medicis, Anna Maria Luisa, who willed the family's art collection to the people of Florence at her death. We have her to thank for the richness of the Uffizi and its 16th-century service tunnel. Now Michele, our minder, opens a door and suddenly Roberto and I are in the grounds of the Pitti Palace, emerging like Alices from a most curious adventure. All the years I have walked across the Ponte Vecchio and never paused to wonder about the structure above or why it disappeared into the Uffizi. Now I know, but will anyone believe me?
How to get there
Abercrombie & Kent (0845 618 2213; abercrombiekent.co.uk) offers three nights' b&b at the five-star Helvetia & Bristol from 996 per person, based on two sharing, including return flights, transfers and a half-day walking tour of Florence that takes in the Uffizi and Vasari Corridor accompanied by a private guide
Further reading The story of seeing Florence without the right guide is told in EM Forster's classic tale 'A Room with a View'