Mittagong Mushroom Tunnel
Nestled beneath Mount Gibraltar near Mittagong in the Southern Highlands of New South Wales is a Victorian-era single-track railway tunnel that today houses racks of cultivated exotic fungi. The Mittagong Mushroom Tunnel (sometimes called the Mount Gibraltar tunnel) is a surviving piece of 19th-century railway engineering that has had at least three distinct lives: as part of the early Main South railway, as a wartime defence/storage facility, and as a commercial mushroom farm and visitor attraction.
Construction and 19th-century railway use
The tunnel was built in the 1860s as part of the Main South line linking Sydney with the southern regions of New South Wales. Construction of this early section of the line took place in the mid- to late-1860s with the Picton–Mittagong portion of the route opening in 1867. The tunnel runs beneath Mount Gibraltar allowing the rail alignment through the Redbank/Mount Gibraltar ridge. As an early Victorian masonry tunnel, it reflects the stone and brickwork techniques used during that period. The line and its tunnel carried regular passenger and freight traffic through the late 19th and early 20th centuries.
As rail traffic grew and engineering standards changed, the original single-track tunnel eventually became a constraint on capacity and operations. A newer double-track deviation (and later alignments) were constructed adjacent to or replacing the original alignment, and the single-track Victorian tunnel was taken out of primary service in the early decades of the 20th century. After rail services were diverted to the newer alignment, the old tunnel stood disused but largely intact, protected from weather by its robust masonry lining.
Decline, Redundancy and Interwar Years
Once redundant to mainline operations the tunnel sat mostly unused for years. Its cool, damp, dark interior proved ideal for storage and later cultivation activities, which is why the disused tunnel attracted non-railway uses after it fell from traffic duties. For many such Victorian tunnels, redundancy often spurred re-use rather than demolition; the Mittagong tunnel survived thanks to the solidity of its construction.
World War II — Defence Store
During World War II the Australian defence authorities repurposed several disused railway tunnels across New South Wales for secure storage, and the Mount Gibraltar/Mittagong tunnel was among them. The tunnel’s naturally cool, dry, and concealed environment made it suitable for housing military stores and munitions. Several disused tunnels in the state became ammunition and defence stores and used through the war years.
Post-war conversion — mushrooms move in
After the war, the tunnel again fell into civilian hands and, from the 1950s onward, was one of the early Australian sites adapted for mushroom cultivation. The physical microclimate of the tunnel with consistent cool temperatures, high humidity, and stable low light closely mirrors the environments where many edible and medicinal fungi naturally thrive, so it proved an excellent place to cultivate button, Swiss brown and later more exotic Asian varieties. In the late 20th century, a mycologist-led enterprise expanded operations and introduced a range of gourmet species to Australian markets; guided tours for visitors became an additional feature of the site.
The tunnel’s conversion into a commercial mushroom farm demonstrates an efficient adaptive reuse of industrial heritage: the same features that made it a useful wartime store made it ideal for fungi production. In addition, guided mushroom tunnel tours combining fungal production with education about mycology and heritage architecture are run on site.
The Mittagong Mushroom Tunnel Tour
The current operators of the tunnel Fungi Co, provide guided tours of their operation. The tour started at the Southern Highlands Visitor Information Centre where we were met by our guide. Following her in our car we soon arrived at the tunnel where the tour began. Our guides then ran through a history of the tunnel from its construction, use as a store in World War Two and now as a mushroom farm.
Walking inside is an experience that feels equal parts industrial archaeology and natural wonder. The temperature drops noticeably as you enter, the air cool and moist which is perfect for mushroom growth. The tunnel’s walls are lined with shelves of yellow, grey, white, and brown fungi. We saw shiitake, oyster, and lion’s mane, sprouting in thick clusters.
Our guide explained the art and science of mushroom farming. The explanation covered how spores are propagated, and humidity and airflow managed. Mushrooms don’t need sunlight, but they do need patience, cleanliness, and a perfect balance of moisture and nutrients.
Inside the Tunnel
The quality of the sandstone blocks lining the lower section of the tunnel walls is impressive. Each is finished beautifully, even though most would never be seen. The photo below shows one of the escape alcoves, intended for use by anyone stuck in the tunnel as a train approached. The attention to detail even for this rarely used alcove is wonderful, with the radiating interlocking blocks at the top.
Remnants From Military Use.
About halfway along the 650m tunnel, corrugated iron lines the ceiling. The Air Force placed this during the Second World War, the keep moisture from dripping on the items stored there. Additionally wooden beams with electrical insulators are all that remains of the militaries’ communication lines and power supply.
Water Damage and Discoloration
At several spots, water has been seeping through the bricks lining the upper portion of the tunnel’s walls. This has left a beautiful colouring where algae, wild fungi, and rust have formed.
Tunnel Exit
After a 650m walk, we left the tunnel and saw the opposite exit. This is not as overgrown as our entry point and the date stone 1866 can be clearly seen.
Mushrooms
Surrounding us throughout the tour of course was a variety of fungi. Currently under cultivation were yellow and grey oyster, lion’s mane, and shiitake. In the wild these mushrooms grow on fallen trees, but when cultivated live in sawdust. Once mixed with spores the sawdust is placed in a calico bag and left to grow on the many shelves in the tunnel. Once the fungi fruits and has reached the correct size it is harvested. The calico bag and contents can then be reused as a second crop will often sprout when rehydrated.
Once the sawdust has been exhausted of its nutrients it is recycled as mulch.
What Did We Think?
This was an excellent tour and highly recommended. Whether fungi farming, railway history or both are you interest this will suit you. The tour was extremely informative, both from the historical perspective of the tunnel to the intricacies of mushroom farming. We had a fantastic time thanks to the friendly hosts and their wealth of information.
To book a tour, go to Fungi Co website, or click here.
To see what else there is to do in New South Wales, please see some of our other stories.
Leave a Reply