While Jack of Watson was recently exploring on the lower slopes of Mt Pleasant, he was surprised to discover, amongst a thicket of blackberries, an abandoned concrete building.

Jack says it is just east of the historic Duntroon Dairy. Although there are signs of it being used as a humpy, the secluded structure, which is about the size of a garage, seems to have been neglected for decades.

"Strewn over the damp floor is discarded clothing, candle wax and books, including a well-read copy of Happy Despatches - journalistic pieces from Banjo Paterson's days as a war correspondent," Jack says. He "would love to know the original purpose of the building".

When your Akubra-clad columnist quizzed Duntroon authorities about the secret structure, they responded, "we have reviewed historical records and have been unable to confirm the history of the abandoned building".

Archival plans subsequently obtained by this column indicate that the concrete bunker was a circa-1920 pump house, initially designed to pump fresh water from the Molonglo River, presumably to the Royal Military College Duntroon (founded in 1911). It was repurposed in the 1940s to house part of Duntroon's expanding sewerage infrastructure.

While the derelict pump house now commands million-dollar views across the Jerrabomberra Wetlands and to the Kingston Foreshore, I'm not sure it'd be the most comfortable place to bury your nose in a book about Australia's military history, especially with the frigid weather we've shivered through this week.

Over recent months, Shaun Casey of Queanbeyan has been carting dirt into the old Pialligo stone quarry near the airport.

"Along with several other truckers I'm curious about several abandoned concrete dugouts scattered throughout the adjoining paddocks," he writes.

"We each have our own theories as to their purpose.

"One of the drivers even reckons they might be part of a tunnel to an undisclosed top-secret location.

"We would love to know the real reason they are there."

Far from being part of some secret-squirrel operation, I can confirm the bunkers (there are five in total) are actually bomb dumps constructed during World War II in response to the prospect of Japanese invasion of our south coast.

They are even listed on the Australian Heritage Database, which states, the structures "are important aspects of Canberra's defence history, illustrating the entry of Japan into the war and the location and operational role, in coastal defence, of three squadrons of the Netherlands East Indies Air Force, Nos 18, 119 and 120 at RAAF Base Fairbairn."

The site is owned by the Commonwealth and privately leased, but it's a pity there isn't an interpretation sign to highlight the site's significance to perplexed passers-by like Shaun.

SouthCare Rescue chopper pilot Bryce England has "long wondered" about the original purpose of a bare patch of land located near the SouthCare base, between HMAS Harman and the Alexander Maconochie Centre.

"From the air, there is a clearly defined square boundary with an old bitumen road and turning circle leading up to it, but it's completely devoid of any structures," Bryce says.

"Google Maps labels the nearest access point as Bonshaw Road."

It's the name of this road that provides a clue to the site's original purpose - the Bonshaw Receiving Station. It was a naval communications complex, managed by the Department of Defence until its closure in 2005. It housed watchkeepers who listened for messages from ships on the high-frequency bands.

Due to the site being key habitat for vulnerable Grassland Earless Dragons, Golden Sun Moths and Striped Legless Lizards, the land is now managed by ACT Parks and Conservation as a natural temperate grassland restoration site.

Several readers have asked about the purpose of the bunker beneath the Uluru Loop at the western end of the National Museum of Australia car park. Due to the amount of rubbish inside, it appears abandoned.

"It's got electricity and lights and would make a great underground venue for a party if it wasn't for the [usually] locked gate," one reader suggests.

When contacted by this column, the museum was unaware of the tunnel's purpose, and with no signage evident on the tunnel, apart from a mobile phone number which, when called is answered by someone who confesses to have surreptitiously used it as his boat shed, it took some time to get to the bottom of this one.

It turns out that it's actually an Icon Water tunnel to provide access to one of Canberra's most important manholes, the Acton Syphon.

"When the [museum's] Uluru Loop was constructed in the early 2000s, the bunker tunnel was installed in order to provide access to the Acton Syphon which takes sewer flow from parts of north Canberra under Lake Burley Griffin," Icon Water's Tony Steeper says.

"Canberrans see water and sewerage infrastructure like the bunker tunnel on a daily basis, but often we don't notice them.

"In the same way as water reservoirs on suburban hills, and sewer manholes in the footpath, such infrastructure is simply part of Canberra's urban landscape.

"So, a fairly prosaic answer to your mystery, but an important one for public health and convenience," Tony quips.

Warning: Public access to all four abandoned sites featured in this column is not permitted without permission from relevant authorities.

It seems that a Gungahlin letterbox isn't the only unusual place Canberra birds have been nesting. John Bundock reports that, "in September 2016, a masked lapwing tried to nest on a tiny patch of grass in the Tidbinbilla Nature Reserve Visitor Centre car park".

"The first egg was removed by a ranger and the second egg didn't last long, being smashed by someone getting out of a car," John says.

"The bird then gave up".

I'm not surprised.

Still in the avian world, Peter Keast, of Torrens, reports that about 18 months ago while walking his dog Max near the local oval, he "noticed a magpie with a damaged wing that couldn't fly".

"Max started to chase the bird but boy could she run, and even after I called Max back, the magpie, with damaged wing outstretched, kept on running away," Peter says.

From that day on Peter kept a close eye on Gammy, as he'd affectionately named the flight-challenged magpie.

"Amazingly, she was there every day and always running from perceived danger or fright," he says.

"She would hide under bushes or scramble from low limbs and eventually clamber up a tree to roost or find safety."

When Peter noticed Gammy attempting to build a nest last spring, he decided to help her out.

"I took bits of string, old zip ties and strapping down to the oval and left it on the ground near her tree," Peter says.

"After clambering with difficulty up and down the tree for weeks, eventually the nest was complete and soon after a baby magpie hatched which resulted in a massive increase in her workload.

"Can you imagine how often she had to climb up and down the tree to feed that ravenous chick."

Despite her inability to fly, ever the determined mother, Gammy successfully reared the chick and according to Peter "is still hopping around Torrens Oval".

Ah shucks, how I love a happy ending.

CONTACT TIM: Email: timtheyowieman@bigpond.com or Twitter: @TimYowie or write c/- The Canberra Times, 9 Pirie St, Fyshwick.

Clue: Excitable kangaroos

Degree of difficulty: Medium

Last week: Congratulations to Nathan Leonard of Garran who was first to correctly identify last week's photo as part of the Dickson Library, designed by architect Enrico Taglietti who sadly passed away last month, aged 93. The chimney-like structure is actually a downpipe that is open at the bottom and allows rainwater to pool before draining away.

"I grew up in Hackett in the 1970s and '80s and spent hours at the library as a kid," Nathan says.

"I always thought it was such an ugly building and didn't really appreciate it until later in life".

Enrico designed many other public buildings in Canberra, such as the Italian Embassy, the Australian War Memorial's annex in Mitchell and several schools including Gowrie, Flynn, Latham and Giralang.

The photo was submitted by Anna Howe of Hackett who confesses to having "an interest in planning and urban environments" and admired many buildings designed by Enrico in the 1960s-70s.

"It's a pity we don't have any distinctive designs since, so we could see when suburbs developed by their architecture," she laments.

How to enter: Email your guess along with your name and address to timtheyowieman@bigpond.com. The first email sent after 10am, Saturday 1 June, 2019 will win a double pass to Dendy - The Home of Quality Cinema.

While Jane and Kim Malcolm of Kambah were recently enjoying a break in warmer climes at Toowoon Bay on the NSW central coast they spotted this owl peering back at them.

"It looks like it was 'created' after a branch snapped off the tree, and thankfully when the top of the tree was later cut off, the owl-like scar remained," Jane, who also spotted a real owl in a nearby tree, reports.

I don't know about you, but I think it bears an uncanny resemblance to the Belconnen Owl, only that the Malcolms' owl leans to the right whereas the infamous Belco sculpture leans towards the left. But, best we leave politics out of it.