My guide is a Russian woman, Katerina Panayatova, who followed an Italian man to Milan, fell in love with the city instead, and decided to stay on even after the affair was over. She asks me to meet her outside the church of Santa Maria delle Grazie, which houses the painting The Last Supper.

As the crow flies, the church is just under two kilometres from the primary railway station, Milano Centrale, but walking to Santa Maria delle Grazie will take time. If you are not up to it, it makes sense to take Milan's underground railway system, Metropolitana, to Cardona, the closest station to the location.

Santa Maria delle Grazie is one among many churches that dot the Milanese landscape, but with one distinctive difference: its connection to Leonardo da Vinci's The Last Supper, preserved inside its refectory (dining hall).

I was one among a group of 20 visitors who were allowed into the refectory. The room is equipped with devices to maintain constant temperature and humidity. The painting (not a fresco as it is painted on a dry wall) is itself protected by a metal barrier and visitors are allowed to view the painting that's roughly 15 feet by 29 feet at a distance. It covers the end wall of the dining hall. We were allowed a mere 15 minutes before we were shepherded out of the room. Some chose to pray while others studied the painting in detail in an attempt to unearth the mysteries embedded in it.

The Last Supper, commissioned by Ludovico Sforza, the Duke of Milan, depicts Christ and his disciples at the dramatic moment when Christ reveals that he is aware of the betrayal, and is one of the world's most iconic images. It displays specifically the reaction of each of his 12 disciples (the Apostles) when Jesus announced that one of them would betray him. Leonardo seats all the diners on one side of the table so that the viewer can have an unhindered view of their expressions. Among them are the most famous, Peter and John, but also the villain, Judas, in blue and green, looking withdrawn and taken aback that Jesus knew of his plan.

Katerina asks us to observe the figure that is set aside from the rest of the group. "Leonardo demarcates Judas Iscariot by having him lean back into shadow; his face, unlike that of the other Apostles, is not illuminated; he is literally lost from Christ's light," she says. He is seen clutching a small bag, which may have been the payment for his betrayal of Jesus, and is depicted as knocking over a salt cellar, which signifies bad luck, and is associated with salt in general.

Leonardo began work on The Last Supper in 1495 and completed it in 1498. He did not work on the painting continuously. It is said that da Vinci's The Last Supper uses the faces of actual people to stand in for the Apostles' faces. Leonardo is said to have loitered around jails and spent time with Milanese criminals to find an appropriate face and expression for Judas.

The painting contains several references to 'The Holy Trinity' - the Apostles are seated in groups of three; there are three windows behind Jesus; and the shape of Jesus's figure resembles a triangle. By the early 16th century, the paint had started to flake and decay, and within 50 years, The Last Supper was a ruin of its former glory. Early restoration attempts only made it worse.

Katerina mentions that in 1652, a doorway was added to the wall, which now holds the painting, and a lower central part of the painting that included Jesus's feet was lost. During the Napoleonic Wars, Napoleon's soldiers bunked in Santa Maria delle Grazie. When they got bored, they used The Last Supper for target practice with Jesus's face as the bullseye. During World War II, the refectory was struck by Allied bombing; protective sandbagging prevented the painting from being struck by bomb splinters, but it was damaged further by vibrations. Finally, in 1980, a 19-year restoration effort of The Last Supper began, but in the process, little of da Vinci's original brushstrokes remained.

As we walk out of the refectory, Katerina relates some of the dozens of conspiracies surrounding da Vinci's The Last Supper. There are new claims that the painting contains a hidden image of a woman holding a child. In 2007, a computer noticed the placement of the bread rolls in the painting looked like musical notes and developed a 40-second musical score. Perhaps the most famous conspiracy popularised in The Da Vinci Code suggests that the person seated to Jesus's right in the painting is Mary Magdalene. But to me, the painting will remain one of the most revered works of art in the world. To see it, you must book in advance or sign up for a guided tour.