An abandoned subway running beneath King William Road, tunnels connecting CBD government buildings, wartime bunkers that later became venues for sex workers — telling stories in Adelaide about tunnels beneath the city is nearly as popular as asking what high school you went to.

Underground myths (and facts): An abandoned subway near North Terrace

An abandoned subway near North Terrace Tunnels connecting CBD government buildings

Tunnels connecting CBD government buildings Underground tunnel access to Parliament

Underground tunnel access to Parliament A CBD network of large sewers and drains

A CBD network of large sewers and drains An underground stream in Adelaide's East End

An underground stream in Adelaide's East End WWII bunkers and secret tunnels

The problem is, few of these stories have been conclusively verified — or ruled out — and save for the tourist attraction of the tunnels beneath the Treasury building, Adelaide's supposed network of subterranean passages, if it exists, remains buried in mystery.

You asked us to find out where the tunnels were, and so, donning my investigative hat and wielding a shovel of curiosity, I started digging up the past.

In the first of our two-part series, I look at the myth surrounding an abandoned subway beneath the CBD's north, tunnels connecting CBD government buildings, and underground access (or escape) from Parliament House.

The brewery beneath The Lion Hotel in North Adelaide is today used as a function space. ( ABC News: Malcolm Sutton )

An underground subway

Perhaps the most common suggestion is there's an underground train tunnel running from the East End to Parliament House.

It's often followed by assertions there was an abandoned plan to build a subway in the City of Churches — nicknamed such in the 1800s, by the way, not due to its large amount of churches but because it was founded on the principles of religious liberty and tolerance.

There were indeed plans for a subway in Adelaide, and there still are — should its population ever grow large enough to warrant it — but the idea of a tunnel already being there from an earlier effort is, unfortunately, incorrect.

State Library of SA content librarian Mark Gilbert said a railway was laid in 1886-87 from Adelaide Railway station to the old Exhibition Hall, which sat on land now occupied by the University of Adelaide alongside Frome Road.

The so-called Jubilee Line passed through what was originally built as a cattle creep, or bridgeway, beneath the raised embankment of the city bridge (now King William Road) that was constructed by 1855 to span the River Torrens.

This section of a famous 1876 Sydney News illustration clearly shows at its centre the short tunnel beneath King William Street. ( Supplied: State Library of South Australia )

But it was only a very short tunnel, with the rest of the railway travelling above ground behind Government House and onto the showgrounds. It was extended to Old Parliament House by 1919 but pulled up in 1927 after the showgrounds were relocated to Wayville.

The short tunnel beneath King William Road was rediscovered in 1973 and for a time Adelaide City Council considered restoring it as a decorative pedestrian subway to the Festival Centre — until it realised it would cost up to $140,000.

It was quickly filled with quarry rubble.

But for those still dreaming of a future subway, if you look to the north side of the new Royal Adelaide Hospital you will see an access slope reportedly built in preparation should a subway ever go ahead.

The Jubilee Line can be seen on this 1919 map (indicated below the blue line) running from behind Parliament House to the Exhibition Grounds. ( Supplied: State Library of SA, reference C196 )

Government tunnels beneath the CBD

Another common belief is there is a network of tunnels beneath Adelaide's CBD connecting government buildings.

The National Trust of SA runs tours of the tunnels or spaces beneath Treasury on Flinders street, which I visited with my principal Curious Adelaide questioner Molly Gifford — I say principal because more than 20 people asked various questions about tunnels.

Molly Gifford stands in the passageway connecting the Treasury basement to the old survey department. ( ABC News: Malcolm Sutton )

The old Treasury Vault is connected by a thin passageway to the basement of what was the old survey department where lithographic processing was undertaken for the production of maps.

Beyond that, it becomes the swimming pool for the Medina hotel.

It is often believed that another tunnel went west from the Treasury Vault beneath King William to the General Post Office (GPO), while another went south beneath Flinders Street to the Torrens Building.

The vault does indeed include a bricked off passageway that appears to head south towards the Torrens Building.

Walter Marsh from the National Trust of SA said he'd recently visited that building's basement and found "quite an impressive underground area that runs the full quadrangle of the building".

Molly Gifford visits the Treasury Vaults, which were stormed by about eight men during the 1931 meat riots. ( ABC News: Malcolm Sutton )

But he added a lot of spaces beneath government buildings were filled in to save costs.

"It would have been difficult to predict, I'm sure, back in the 1800s, that these sort of underground passages or basements would have this mystique 100 or more years down the track," Mr Marsh said.

"It would have been nice if they kept a few more of them."

Molly checks out an underground space used by bars and businesses on Leigh Street. ( ABC News: Malcolm Sutton )

A friend of mine who once worked inside the old Trims building on the corner of Halifax and King William streets said its basement also included a tunnel entrance.

The owners of the site, which is now under development, would not allow me access to explore this prospect but my friend said it appeared to head west beneath King William Road towards the Kings Head Hotel.

A staff member at the Kings Head assured me there was no tunnel arriving in its own basement.

Undeterred, Molly and I tried to visit a tunnel we'd heard existed under Hindley Street.

After a little guidance from those working in the area, we found a large basement-like structure beneath Leigh Street used by businesses for storage.

I also investigated the old tea rooms beneath Adelaide Arcade and the old brewery tunnels beneath The Lion Hotel in North Adelaide.

They were impressive, but nothing I saw resembled the sort of mystical, secret tunnels clearly believed in by so many questioners on Curious Adelaide.

A basement space beneath Adelaide Arcade was once used as tea rooms. ( ABC News: Malcolm Sutton )

A tunnel from Parliament

At Old Parliament House I was granted access to its basement (now a plant room) to view a bricked-off doorway heading south into the CBD.

Labelled an old store room by authorities, the rumour is a tunnel travels deep into the city from Parliament and perhaps all the way to the GPO or Treasury.

This tunnel extends north from Parliament House but ends somewhere beneath Festival Plaza. ( ABC News: Malcolm Sutton )

Parliament House Serjeant at Arms Paul Collett was doubtful about the tunnel but diplomatically offered that the idea "was not a myth" because "it cannot be proved" it wasn't there.

"But on top of it is the chambers, the library and all that sort of stuff, so quite simply, it would have been an area used for storage, cooking, cleaning, all that stuff," he said.

At the back of the main building, which the Government started building in the late 1880s to replace Old Parliament House, Mr Collett showed me an old passageway heading south towards the Festival Centre.

The passageway is believed to have been used as an access tunnel for those working at Parliament House up until the 1970s when the Festival Plaza was developed.

"If you ripped up the floors in the main building, in the main chamber, you'd probably find some [tunnels], but it just doesn't work like that," Mr Collett said.

"Everything's been taken apart, put back together, with no regard for keeping the old stuff."

Steps from the Old Parliament House plant room lead to a closed off doorway that once headed south into the CBD. ( ABC News: Malcolm Sutton )

Further east there is a large complex of tunnels beneath the former Royal Adelaide Hospital. They connect the north wing and the services block and travel through to the residential wing.

Former RAH chief executive Professor Brendon Kearney said there was also a large amount of service tunnels, electricity ducts and the like but they all stayed within the perimeter of the building and did not extend into the city.

"There's a lot of talk of those things, but in 15 years as CEO, and having been all over the place over the years, I've never seen anything," he said.

The State Library of SA's Mark Gilbert said librarians were consistently asked about Adelaide's tunnels.

"But there's no real further information that we ever find," he said.

"It would be great if we could because it's a great story. I'd like to be the person who discovers something about it and put it on our Facebook page as though it's a brand new story."

State Library of SA content librarian Mark Gilbert says questions about Adelaide's tunnels were common for librarians. ( ABC News: Malcolm Sutton )

Trust no-one

Being a cynical, somewhat bitter journalist, I'm happy to say I rarely believe what "the man" says, and you shouldn't either.

Legitimate questions remain about the Old Parliament House tunnel, and those that may or may not surround the Treasury Vaults.

I've no doubt that somebody out there knows a lot more than I've been able to find out and they may even have a key.

In the meantime, never stop believing.

Join us next Friday as I plunge into Adelaide's sewer and stormwater networks for part two of this investigation, and find out about giant rats causing chaos in wartime bunkers.