This may be a Royal Library but it is currently honoring the greatest artistic and scientific mind of the Renaissance, Leonardo da Vinci.

The library's director, Giovanni Saccani, leads me down to the "caveau" - a high-security vault that's been carefully designed to preserve but also display the precious treasures in the collection.

This is where Leonardo's drawings and the rest of the royal collection normally reside in drawers and containers behind display cases. The lights, says Giovanni Saccani, are exclusively fiber optic.

Having just descended from the warm wooden library above us, the dim grey hues complement the reverent chill in the air down here.

"The ideal temperature is around 20 degrees, with a tolerated difference of 2 or 3 degrees more or less," says Saccani. "The percentage of humidity has to stay around 55, again with a 5 percent tolerated margin each way. Right now we are keeping the temperature a little lower to allow for the increase in temperature and humidity which the huge number of visitors inevitably makes. This will ensure we always remain in this ideal range for preservation."

A most famous selfie

From 9am till 6pm 7 days a week, until mid January, 50 people per hour will visit the caveau.

The exhibition's packed with invaluable works by renowned artists like Raphael, Perugino and Van Dyck.

Leonardo's Codex on the Flight of Birds is in here too but, for most, the highlight is the chance to set their eyes on that famous red chalk self-portrait.

The image is strikingly intense, in spite of its poor condition.

Using a special conservation torch, Saccani points out the extensive damage it's suffered over the centuries.

"Foxing is these little dots, these marks. You normally find foxing on very old paper. Unfortunately the self-portrait is riddled with it, probably because of the nature of the paper itself," says Saccani.

But he says the world's top experts agree it's too risky to try to restore it.

"It was decided that the best thing to do was to maintain the status quo. The only thing they suggested - which wouldn't cause any damage, only improvement - would be a conservation measure using dry, non-invasive techniques aimed simply at cleaning the paper."

Analyses confirm that the drawing's condition hasn't deteriorated further since it was moved down here 15 years ago.

Purpose-build home

Giovanni Saccani believes this is the only such purpose-built home for an artist's works in the world.

One of the architects who designed it back in 1998 is Stefano Trucco.

"The idea at the time was to build Leonardo One. Twenty-five years ago, where we're standing was a sort of derelict basement with earth on the floor," says Trucco. "You went in through a grill and had to jump down off a wooden ladder. It was full of cats and completely abandoned."

Trucco calls this Leonardo One because his team's just finished building Leonardo Two - a slightly larger caveau on the other side of the stairwell.

He points out some of the technological details that went into designing these vaults to make it possible to exhibit even the most delicate work in the collection.

"We've put a temperature and humidity control system in each one of these display cases. They can be individually controlled, even at a distance from the director's office," says Trucco. "You can see it here - that little white box is a detector, and there's one in every window. This whole system was devised so that even if the spaces around the cases are subject to strong changes, thermal inertia ensures that whatever is behind glass won't be subject to the temperature changes in the rest of the room."

Travel ban

While Leonardo's self-portrait is probably the most priceless and fragile work on show, the others are of extraordinary value too. Giovanni Saccani describes the glass of the display cases as "anti-everything."

As well as having reinforced doors and walls, the rooms are protected with security cameras and alarms.

You would think such valuable works would never leave the caveau but, in fact, Leonardo's Codex on the Flight of Birds travels quite regularly.

Since 2012 it's been to Moscow, Washington and New York, and will go to Japan for the first time in 2016.

But the self-portrait is a different story. Because of its fragile state and exceptional value, it's subject to a state decree of immovability and can't go anywhere without ministerial permission. In 2011, when it was exhibited just outside Turin for the 150th anniversary of the Unification of Italy, the process was excruciatingly complex and costly.

"Special transportation containers called 'clima-boxes' were used. They maintain the same conditions as we have in this room," says Saccani. "The clima-box was put inside a case which was in turn placed in an outer casing, all of which could avoid vibrations, even during the journey. There was an armed escort and a WiFi data-logger system allowed 24-hour temperature and humidity monitoring."

Understandably, Giovanni Saccani says there are no plans to attempt to move the self-portrait again in the near future. But, he smiles, there is a digital reproduction of it on NASA's Curiosity Rover, which is roving around on Mars.

The exhibition runs until January 15, 2015.