The idea there's a network of hidden or forgotten tunnels beneath Adelaide has long sparked conversation but, as we discovered last week, much of it's based on myth or exaggeration.

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

What Adelaide does have, however, is a stormwater network and one or two larger sewers — not to mention a number of wartime bunkers and trenches.

And so, donning my coveralls and recruiting the services of an equally adventurous ABC cameraman, we ignored the stench and plunged into darkness for this second part in our Curious Adelaide investigation into Adelaide's tunnels.

Zorga's Tomb and ninja turtles

Of more than 20 Curious Adelaide questions submitted about tunnels, one asked where Zorga's Tomb ended.

Zorga's Tomb is one of Adelaide's longest stormwater drains and exists in the same region of the city as others, such as Adelaide Darkie (Darkies) and St Peters Twins.

A Google search of these names reveals many photographs of the city's concrete drain network — thanks largely to secretive urban explorers, Cave Clan, a movement that started in Melbourne, or the informative website, Awesome Adelaide.

Zorga's Tomb was named by the pioneer of Adelaide's urban explorer movement, Eughan "Zorga" Cameron, who passed away last decade.

A fellow explorer who goes by the name Lite, said Zorga inspired him and his friends to check out Adelaide's underground spaces.

"There was a photo in the Advertiser in the early to mid 1990s of a guy standing in this brick, arched drain, and a friend of mine and I said, 'Hey, let's go meet that guy and see what's down there'," Lite said.

"Zorga really pioneered the whole effort in Adelaide, contacted the Melbourne guys and got the scene moving here."

I found these drains and undertook a little exploration. I cannot reveal their exact location as drains are dangerous, particularly in wet weather, but I can tell you they are not in the CBD but the inner suburbs.

Another hope for tunnels in Adelaide is in its sewer network and the idea there might be a complex of tunnels.

Drains such as Adelaide Darkie are a popular location for urban explorers but should never be visited in or after wet weather. ( ABC News: Malcolm Sutton )

A 1929 image taken of an oviform pipe in the Glenelg area of the metropolitan sewer network. ( Supplied: SA Water )

SA Water's biggest wastewater pipe is the Bolivar trunk main. It gets as large as 2.6 metres in diameter before it reaches the Bolivar water treatment plant.

SA Water Wastewater Renewals lead asset planner Craig Williamson said it starts in Adelaide's north-east in the Paradise area, followed the River Torrens into the city, "crossing over the Torrens at one point", before following a train line back out north.

"Back in the 1980s and 90s we had these things called boat chambers, and we've had people do inspections of that trunk main during low flows in the early hours of the morning," he said.

"We certainly haven't sent boats down there for many years now but initially it was designed for that."

The vast majority of the network, however, includes sewer mains that are just 150 millimetres in diameter.

Boat chambers like these were used for maintenance during low flows in some of the larger trunk mains of Adelaide's sewer system. ( Supplied: SA Water )

Mr Williamson said the network included some ovi-form pipes that resembled a smaller version of the types of sewers seen overseas in places like New York or London.

He said such overseas sewer networks could be extensive because they combined both wastewater and stormwater but in Adelaide the two are separated.

Mr Williamson said some ovi-form pipes travel beneath West Terrace, some along the River Torrens, and others in the city's older suburbs.

"Some of those date back to 1880 and they were so well constructed that they're probably going to outlast all of us," he said.

Journalist Malcolm Sutton near the circular entrance of the St Peter's Twins stormwater drain. ( ABC News: Chris Lockyer )

While researching this story, an excited Adelaidean told me of an underground stream he believed existed in the city's East End. When there was a lot of rain, he said the stream rose and caused flooding in the basements of buildings.

Mr Williamson said there was only standard freshwater reticulation mains around Rundle Street/Mall and they reached just 300 millimetres in diameter.

He said basement flooding was likely attributed to stormwater infiltration into sewer mains or, as a less likely cause, poor plumbing in old buildings where internal drains might be connected to stormwater.

Wartime bunkers, shelter and trenches

Bomb shelters and trenches were built across the city throughout World War II, with basic pipe air raid shelters a favourite in places like the Botanic Gardens. There is evidence of these right across Adelaide, including at the Glenelg Football Oval.

Similar shelters along North Terrace became popular havens for ladies of the night to ply their trade.

"There's all sorts of stories about women on Kintore Avenue and so forth," the State Library of SA's Mark Gilbert said.

"And people, young couples on the Torrens, didn't have anywhere else to go, so what can they do?"

Army girls dig air raid trenches in Adelaide during World War II. ( Supplied: State Library of SA (B 21657) )

More extensive shelters were built at the Daws Road Repatriation Hospital for injured servicemen and staff during WWII.

They grew a reputation as courting places for nurses and soldiers but are thought to have been filled in during the 1960s.

Stories have persisted in subsequent decades of staff finding hidden doorways into subterranean rooms with beds and even operating theatres underground.

A recent excavation by Flinders University, however, found only remnants of simple iron and timber shelters connected by a series of tunnels.

"It was more exciting before they discovered it," an ex-Repat worker told me.

A pipe shelter on North Terrace typical of many built across the CBD during World War II. ( Supplied: State of Library of SA )

Another Curious Adelaide questioner suggested a hidden tunnel existed between the former Holden factory at Elizabeth and the RAAF base at Edinburgh.

"I can categorically state there is no tunnel connecting the two sites or connecting our site to any other site," GM Holden corporate affairs manager Megan Lloyd said.

There are, of course, subterranean tunnels associated with Fort Largs and Fort Glanville in Adelaide's western beaches, and part of a network of non-public air raid communication shelters remains visible after being established in 1942.

Prospect Local History Group convener David Kilner said there were eight sub-control centres based around inner Adelaide with those at Glenelg Oval, Prospect Oval, and on South Road at Thebarton still in existence.

The Prospect air raid shelter is still in existence alongside Willcox Avenue. ( Supplied: Prospect Local History Group )

"Their role was to coordinate the civil defence response in the event of air raids," he said.

A final belief regarding the war is the idea a much larger communications bunker was installed beneath Adelaide that would kick into gear in the event of a major incident.

Keswick Military Museum archivist Paul Longstaff said he had never heard of such an installation, despite a photograph on the Awesome Adelaide website picturing what it describes as a communication bunker in rural Adelaide.

The website's operator did not respond to my contact attempts, but it is worth noting Awesome Adelaide reported the tunnel becoming a mushroom farm after the war — the same fate as the Sleeps Hills tunnels in the Adelaide foothills.

The giant Sleeps Hill rat

The 170-metre and 360-metre Sleeps Hill tunnels at Lynton were originally built as railway tunnels during the 1880s.

In 1920 they were decommissioned and replaced by a dual-line tunnel because trains were getting heavier and a purpose-built viaduct for trains at the other end of the tunnels was no longer strong enough.

Air-conditioning ducts are still visible from the Sleeps Hill tunnels' days as mushroom farms. ( ABC News: Malcolm Sutton )

The tunnels, which are believed to be eight layers thick with purpose-built bricks, were used during WWII to store artwork and government documents for safekeeping in the event of a Japanese bombing attack.

"There's a story getting around that there was a massive painting of King George in storage," Tunnels Wine Storage owner Dave Munro said.

"Apparently one of the sentry guards saw a rat, so there was a bloody big exhibition to try and get this rat because they were worried about the King George painting getting destroyed."

After the war the tunnel was used as a mushroom farm, a venture Dave said eventually cost too much because the mushrooms raised the temperature in the tunnels and therefore required air conditioning.

Mr Munro now owns the tunnels and utilises one for commercial wine storage due to the fact it sits at a stable 17 degrees Celsius.

The bricked tunnels are believed to be eight layers thick. ( ABC News: Malcolm Sutton )

A final tunnel-related question on Curious Adelaide involves the small, grill-covered tunnel that penetrates the cliff face alongside Gorge Road and the Torrens River in the foothills.

SA Water's Craig Williamson said it is likely to be connected to a trunk water main with a 750-millimetre diameter pipe running from Kangaroo Dam.

Archways beneath Adelaide Casino

The archways are likely remnants of the old Adelaide railway station, which the new station was built on top of. ( Supplied )

In response to last week's article, we received several messages and information about other tunnels, from Yorke Peninsula hotels, to the cliffs near Seacliff.

We also received an interesting photo of three archways beneath Adelaide Casino that were uncovered during the Festival Plaza redevelopment.

They are not evidence of an abandoned subway, but likely remnants of the original Adelaide Railway Station, which first opened in 1856.

It was rebuilt in 1900 with a dual entrance and domed covers for railway platforms, then replaced by the much larger and extravagant railway station of today, opened in 1928.

Part of that station was repurposed for the Adelaide Casino, which opened in 1985.

On discussion with the State Library of South Australia's Mark Gilbert, it was determined that the archways found packed with sand beneath the casino were most likely entrances to a storage shed for engines in the old railway yards.

Adelaide Railway Station as it appeared in about 1873 with North Terrace buildings behind it. ( Supplied: State Library of SA, reference B-3741 )

The truth is out there

I've no doubt there will be hidden spaces and vaults beneath Adelaide's buildings, hotels and even government establishments that I haven't peered into during this investigation.

I don't delude myself by considering my search to be exhaustive and, as I said last week, believe there are more to be found.

There is of course a difference between an underground space and a tunnel — the latter being a passageway that connects one space to another.

Should you find a bricked-off doorway or remnants of a tunnel crawling off to another subterranean den, pay attention: You may have just found a missing link.