Imagine dropping through a small hole in the middle of the roof of the Millennium Stadium. You are descending on a swinging wire ladder into a watery world of unfathomable darkness, as the walls immediately and dramatically recede in all directions.
     Above your head is a 1m-diameter hole through which a narrow shaft of sunlight forces its way. Your eyes struggle to adjust to the light levels and your heart beats faster, not only with the effort of climbing but at the thought of what lies beneath.
     This is the Shaft, one of the true wonders of the diving world and perhaps the most infamous cave site in Australia.
     The entrance to the Shaft is in the middle of a huge, flat field in the middle of nowhere. There is no indication of anything unusual, until you find a heavy steel grille. Overhung and obscured by lush grass, you could find it only by using a GPS co-ordinate or following very detailed instructions.
     Cows momentarily lift their heads nearby as large quantities of dive gear are strewn around what can be best described as a simple drain cover.
     Kitted out with a climbing harness and attached to a sturdy nylon rope, your stomach begins to churn.
     Guide Gary Barclay has been here many times and takes it all in his stride: Just dont drop anything; well lower your cylinders down once youre in the water, he says.
     Seconds later, the normal world of light and warmth is gone, replaced by the dank gloom one associates with a castle dungeon. Apprehensions mount. Eight metres down, you land in the water and feel very, very small!

Australia is a BIG place. The scope for diving is huge, with a variety of sites rarely equalled. The Great Barrier Reef of Queensland is renowned but few will appreciate the delights of inland diving. Places such as Mount Gambier possess the clearest water in the world.
     The Shaft lies in the Mount Gambier region, the extreme south-eastern corner of South Australia, near the border with Victoria. Perhaps the most popular venue for inland diving on the continent, it lies between the two major cities of Adelaide in the west and Melbourne to the east.
     Its a five-hour drive from Melbourne, but the easy access to clear water is a big attraction. I was there between March and April to savour the experience. The weather in the Mount Gambier area can be unpredictable, and January to March are the driest months, June and July the wettest.
     The summer months are generally dry and the most pleasant, with temperatures up to 23ÂC. In summer, a warm thermocline raises the upper 6m of water from 16ÂCbelow to perhaps 21ÂC.
     Its a long haul from anywhere to Australia; the flight from the UK had taken a gruelling 26 hours. On arrival there was the dreaded jet-lag to contend with, but at least the motoring is sensible, driving on the left side of the road.
     Combining the facts that the seasons are quite different in the Southern Hemisphere, it is altogether warmer and drier, and the atmosphere is generally relaxed and friendly, the adjustment is not too stressful.
     The Shaft would provide the crowning memory of our Australian visit. But at the moment, bobbing around on the water, we struggle with our kit and our anxieties.
     We have been thoroughly briefed on the surface and believe we are reasonably prepared to explore the site. At the same time we are aware that the dark void below must rate among the largest underwater chambers in the world.
     When everyone is ready, we drop cautiously into the depths. As the walls disappear, it is very reassuring to reference two prominent decompression lines. At 36m we alight on the top of a cone of rubble, from where the place extends ever deeper.
     The late Sheck Exley explored one side of this monster cave to 80m on a brief visit in the early 90s, while the other side has been followed by the leading Australian diver Christopher Brown to a current depth of 120m.
     Governing body the Cave Divers Association of Australia (CDAA), which kindly hosted our visit, currently imposes a depth limit of 40m at all its sites (see panel), and as we tour this immense cave at this level, we reflect on the reasoning behind this rule. We are all diving on air, yet any narcosis effects seems negligible. It is as though the cave is trying to lure us deeper.
     I also recall that this was the site of Australias worst cave-diving incident. In 1973 four of a group of eight divers perished when, for a variety of reasons, they lost orientation at far greater depths than 40m, ran out of air and drowned.
     Our outstanding memory is of the vision from the back end of the cavern. Using a mirror, someone on the surface is reflecting sunlight into the depths. As this plays on the walls, it focuses our attention on the fact that we can see clearly all the way up to the water surface 40m above.
     With our eyes by now accustomed to the low light level, chains of bubbles rise like smoke from a campfire into a night sky. Contained between narrowing rock walls, they seem to twist and curl in their ascent. It is an ethereal vision, something eternal for the memory yet something that perhaps could never be captured or reproduced in visual form.

The exceptional visibility in the Mount Gambier region comes about because the waters that emerge at Piccaninnie and Ewens Ponds, close to the coast, are drawn from a vast area of limestone which is very sparsely populated. This 14ÂCwater is almost certainly the purest, clearest water on Earth.
     Both Piccaninnie and Ewens are supervised by the local equivalent of our national parks authorities. Platforms and raised walkways minimise disturbance to plant life and silt, so in-water conditions are invariably excellent all year.
     Ewens Ponds is popular with divers and snorkellers alike. In autumn (March, April and May) the flow is minimal, yet sufficiently strong to restore the visibility within a couple of hours. At both Piccaninnie and Ewens you can drift effortlessly amid luxuriant plant life and shallow sand-floored sections.
     As there are no trees to shade out the sunlight, the underwater world sparkles vibrantly, so much so that at Ewens, for example, visitors frequently do the 300m-long section and then do it all over again. Pure bliss.
     But the site of sites in the area is the fabled Piccaninnie Ponds. Here a small floating pontoon provides a dive base and the experience of a lifetime. A broad expanse of reed-flanked pond with depths of around 6m leads to a small section of natural rock wall. Swimming over this, a gaping chasm is revealed.
     From the surface, the sheer drop-off appears like some dark, fathomless trench. This crevasse plunges vertically to 36m before a slight kink occurs in the shaft and it falls away directly to more than 80m.
     Looking down, its possible to see divers plainly at 36m, their chains of bubbles surging towards the light.

While this may be a wonderful place to snorkel, viewed from below water the scene is altogether more fantastic. The depth of blue is purity itself and here the feeling really is that of being suspended in space. Greenery drapes from the sheer rugged walls, partially hiding entrances to shallow cave passages off to the side.
     At the far side of the Chasm lies the Cathedral, a massively sculpted, substantial cavern set in white limestone rock. Shoals of small fish, and some much larger, flit across the ceiling. When they are driven into a silty recess, a small puff of cloud suddenly rolls out into the cavern, slowly dispersing harmlessly in the huge void.
     Framed by the sizeable entrance with its homely, reassuring backdrop of light, a divers lamp pierces the darkness like a laser. To dive here in the morning, with shafts of sunlight breaking through the windows in the ceiling high above, is a spectacular, almost religious, experience.
     For fully certified cave-divers, the systems further inland offer further possibilities. Beneath the town of Mount Gambier lie the intricate passageways of Engelbrecht Cave. This was once the city rubbish dump, but as the town grew to become a thriving tourist centre, the local authority realised the potential of the place.

Today Engelbrecht has been transformed into a show cave and takes great pride in exhibiting its crystal pools to the public. Divers have explored hundreds of metres of superb tunnels and a spectacularly large dry section.
     One particular cavern lies only a few metres beneath houses and a busy highway, and divers can almost hear and feel the rumble of heavy trucks overhead, their drivers blissfully unaware of the immense void just beneath the road.
     The longest submerged cave system in Australia, Tank Cave, also lies in this area. Long known to farmers and a few local enthusiasts as a silty puddle supplying a small windmill, it came as a shock when in 1994 a restriction at the foot of the pool was passed. A magnificent system was instantly revealed, sporting an intricate labyrinth of passages leading away in all directions.
     Much of the cave is less than 15m deep, allowing long bottom times and some lengthy penetrations. More than six miles of crystal-clear tunnels have been charted to date. We were privileged to dive the main tunnels and were left with the impression that this place could extend for many miles more.
     Three weeks diving here was nowhere near enough. Other experiences in New South Wales and meetings with many leading divers simply whetted our appetites to experience the Nullarbor and the mighty caves which lie beneath the barren surface of the interior, in remote areas and as yet undived. Inner Australia is a wondrous place.

  • The Mount Gambier area offers a good range of accommodation from camping to four-star hotels but the Blink Bonney Lodge (bunkhouse) rates highly with visiting divers as the proprietor is a cave-diver and offers information, air, nitrox and rental equipment (0061 8 8723 0879)

  • Youd
    Youd never guess that this spot marks the entrance to one of the worlds most stunning dive sites - the Shaft
    in the Shaft at about 10m
    below the pontoon dive-base in Piccaninnie Ponds
    Piccaninnie Cathedral, a cavern set in white limestone
    In Tank Cave, the longest submerged cave system in Australia
    Engelbrecht Cave, beneath Mount Gambier, was once the towns rubbish dump
    the entrance to Engelbrecht - tours on the hour
    Much of Tank Cave is less than 15m deep, allowing divers long penetrations
    Cave-diving courses are run under the guidance of the CDAA
    A diving permit and appropriate certification is required from the Cave Divers Association of Australia for the majority of sites. The CDAA was formed in 1973, following a series of fatalities in the sinkholes of Mount Gambier (11 deaths in seven years).

    Fear of legal liability prompted land-owners, both private and public, to close the caves on their property to diving. The CDAA united to defend the sport and demonstrate that divers could regulate their activities and develop acceptable levels of safety and training.

    Sinkholes and caves were categorised into three levels of difficulty. Divers were also required to take examinations to access caves at one or more of the three levels. Negotiations with land-owners resulted in contracts guaranteeing that the holes would remain open to CDAA-trained members.

    The CDAA is a non-profit association and uses much of its membership fees to pay legal costs incurred in negotiating arrangements with land-owners.

    The association has developed a four-level training programme complete with standardised notes and instructor programmes and this is under constant review. To access the programme, a diver must have held open-water certification for more than 12 months and have undertaken at least 15 dives, including two night dives. The certification levels are

    Cavern: Start-up, similar to other global programmes: maximum depth 20m, maximum penetration 40m.

    Sinkhole: Similar to above, but maximum depth 40m. Often run with Cavern.

    Cave: Maximum depth 40m, penetration limited to one-third of twin cylinders. Passage size must allow for buddy breathing side by side.

    Penetration: Encompasses smaller passages and stage-diving, maximum depth 40m.

    Contact the CDAA by writing to PO Box 290, North Adelaide 5006, South Australia or go to www.cavedivers.com.au

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