To get there, they drive about 25 kilometres north of Melbourne, to a nondescript industrial park that backs on to a railway line and the fences of a quiet residential outer suburb. There are no signs revealing what's inside but the imposing exterior suggests something very valuable. Perhaps national secrets, or a confidential lab experiment. For once, the reality is just as exciting: the cube is brimming with billions of dollars in cold hard cash. This is the National Banknote Site, Australia's Fort Knox. Despite how you might imagine it, the nation's biggest bank vault does not lie deep beneath the city's streets or in the side of a mountain somewhere.

It is located in the otherwise humdrum suburb of Craigieburn, just off the Hume Highway, where the factories and brick veneer houses turn to paddocks. Loading Replay Replay video Play video Play video Newly built by the Reserve Bank of Australia, this supervault has the capacity to store the entirety of the nation's folding stuff. At last count there were 1.5 billion banknotes in circulation, worth $73.6 billion. 'Like Get Smart' Gaining entry to the vault is, unsurprisingly, very difficult.

On a recent tour, The Age was given a close-up look at the extraordinary levels of security and the way cash is dispensed on the first steps of its journey into our wallets and purses. The man taking us inside is Michael Andersen. As the RBA's head of note issue, he has overseen the first major overhaul of Australia's banknotes since polymer bills replaced paper cash in 1992. The sparkling hi-tech facility was built to coincide with the RBA's release of new counterfeit-proof $5, $10 and $50 notes. Cash may no longer be king, but it is still a significant part of the economy. "There is no sign of it disappearing," he says. The intention of the vault's design, he says, was to create as many safeguard layers as possible. Breaching one in a heist might be possible but getting through all of them would not.

"It's like an onion and no one knows them all," he says. The outside of the National Banknote Site. After handing over our ID at a guarded checkpoint, we are asked to leave our phone behind. Banknotes brought in from the outside must also be locked away, in case they contaminate the supply. Once inside, we move through a series of steel doors, which are activated with a fingerprint scanner or passcode. Only one can be opened at any point and they close automatically with a heavy click. "It's like Maxwell Smart," says Mr Andersen, "and if these doors closed on you, you’d really know about it."

Inside the vault At the heart of the vault is a large room sealed by a heavy gate. This is where the cash is held. Those with fantasies of diving into a pool of riches a la Scrooge McDuck would be a little disappointed. There are no piles of money waiting to be stuffed into sacks by balaclava-clad bank robbers. Rather, the cash is stored inside thousands of custom-designed containers on a hi-tech racking system that looks a little bit like the shelves at Bunnings. Humans are not supposed to be in here.

Instead, red driverless forklifts whiz around picking up the containers and then delivering them to a distribution area. The idea, presumably, being that machines can't be corrupted by greed. An automatic forklift prepares to take a box of money to the distribution area. The grey containers, which are about the size of a large washing basket, can hold up to 100,000 notes each. When full, they weigh 120kg. Each container is secured with multiple tamper-evident locks and labeled with a barcode revealing the wealth inside. A single container of $100s would contain $10 million. And there are pallets of containers everywhere. Would you like cash out?

Bills are moved to the vault after being printed at the neighbouring Note Printing Australia facility, a wholly owned subsidiary of the RBA. The money is then dispensed to banks by appointment, when armoured cars from the various cash-in-transit companies arrive to pick up their order. A $20 bill being checked for imperfections. Once again, robots do the heavy lifting, placing the required containers of cash in a secure, "airlocked" area, which prevents the vault's staff from having any contact with the uniformed drivers. Damaged or counterfeit notes can also be returned by banks to the RBA. Return to sender

Upstairs is the only place at the vault where people get to touch money. This is where suspected unfit bills sent back to the RBA to see if they should be removed from circulation. Here, six large machines are fed tens of millions of dollars in cash that might have been torn, punctured, or faked. Bills are fed into his machine to check if they are unfit. If a dodgy note is detected, it is immediately shredded into confetti-sized pieces and sucked through a vacuum system out to a recycling area. Glints of orange can be seen through one tube as a stash of bad $20s is disintegrated.

From there, the notes are melted down and can be used to make things like plumbing fittings and compost bins. You never know, your worm farm might be made of $100 bills. Checking the cash If the machine can't tell, then the notes are sent across in trolleys to an area to be looked at individually by the RBA's cash experts. Unfit banknotes are destroyed into small pieces before being recycled. In this room, there are cameras everywhere. We're not allowed to say how many or where they are, but it's a lot.

These cameras, Mr Andersen says, are for the RBA's protection and the staff too, as they use UV lights, rulers and erasers to scan for imperfections. Ordinary people can also send back their own damaged notes in the post to be checked, with the bank offering to reimburse those who do so. The reason for people having damaged bills varies but can include tragic circumstances. Mr Andersen says in the aftermath of the Black Saturday bushfires, people sent in tins full of melted notes. Unfit notes after being checked by the RBA. After becoming fully operational last month, it is anticipated that the National Banknote Site has enough capacity to last for another 50 years. It cost between $70-80 million to build and is 14,000 cubic metres in size.