Hundreds of people work in this hidden ‘city’ and you wouldn’t even know it was there

You could walk straight past and not even notice.

As unusual workplaces go, a hidden facility where hundreds of employees head underground to clock in might take some beating.

SubTropolis in Kansas City, Missouri, has millions of square feet of space and is home to workers producing and storing everything from food packaging to cars.

But despite its size, there’s every chance you wouldn’t even know this place exists – because the whole thing is located 150 ft below surface level and has trademarked the claim to be the ‘World’s Largest Underground Business Complex’.

SubTropolis, which has been around since 1964, is located just 10 minutes away from Kansas City’s central business district in Missouri, and 20 minutes from Kansas City International Airport.

The complex itself is actually created from a limestone mine – known as Bethany Falls – believed to be around 270 million years old, with builders using a mining system known as the ‘room and pillar’ method to remove limestone from the complex.

What’s left is a huge underground space with 17 foot high ceilings, propped up by huge 25 foot square pillars.

Just to add to the hugeness of it all, the facility features a network of 40 foot wide tunnels separated by these pillars, complete with concrete flooring. All in all, it has 7.8 million square feet of space for lease and a further 6.2 million square feet which could be used for expansion.

Those who work here can also expect almost 10.5 miles worth of illuminated underground roads, as well as 21 miles of railroad track.

Being so far underground has its advantages – largely the fact that the temperature in SubTropolis is maintained at a steady 18-21°C all year round – and anything stored there is protected from humidity and the elements.

Unsurprisingly, the place is used by a lot of companies as a storage facility, and is also popular with those that use sensitive machinery, as it will not become too hot or too cold.

So which businesses have set up shop in SubTropolis? Well there’s everything from E-commerce, pharmaceutical and animal health companies, through to record storage and food packaging and distribution.

The US Environmental Protection Agency are among those who have leased space here, as well as Ford, the National Archives and Records Administration, and the US Post Office – who use the facility to store hundreds of millions of postage stamps.

Let’s not forget also about Automotive Alley, with the underground facility close to Kansas City’s Ford and GM plants.

Ford was one of the first companies to move into SubTropolis when it opened and long used the space to store old vehicles. These days it’s used mainly for car customisation work.

And food storage companies also make use of the space – with one family-owned catering firm, Paris Brothers, revealing that they used SubTropolis to store such produce as unroasted coffee beans, as well as over 600 varieties of cheese.

‘When we say that these are cave-aged cheese, they literally are,’ co-owner Joseph Paris told CNN, adding: ‘The 55% to 65% humidity is ideal to store our unroasted coffee.’

Other items you’ll find in the complex include tax records and federal court documents from the National Archives and Records Association, as well as the original film reels of Gone With The Wind and The Wizard Of Oz – all of which is stored in the climate-controlled facility to prevent it from degrading.

Currently it’s estimated around 1,600 people work in SubTropolis, which is accessible from street level via a number of different entrances – and the curious can also drive in and take a look around.

It’s not the only underground industrial facility in the US, mind, with Mega Cavern, another former limestone cave turned workplace open for business in Louisville, Kentucky.

But this one is the biggest – and with more space available for expansion, the sky – or at least the underground ceiling – is the limit.