I AM LYING IN MY TENT. Yet again I have woken to a distinctive noise. Before, it was an unsettling but soft pat, pat, pat. Now its a heavy thump, thump, thump, and I pray that it doesnt get any louder.
     We are in the semi-desert of Western Australia, on the Nullarbor Plain. The sound that is giving me the sleepless night is the steady-beating footfall of passing kangaroos. I lie still, hoping that the fast-moving animals can see well enough to avoid the tent.
     I unzip the outer flysheet and peer into the night. The sky is crystal-clear. We had been watching shooting stars earlier.
     The reason for this trip lies 90m beneath us - the largest, clearest and perhaps longest underwater caves in the world. This trip is a lifetimes ambition, a pilgrimage to one of the most challenging places I have experienced.
     The flat, barren and seemingly featureless Nullarbor Plain is the largest area of continuous limestone on Earth. It has the potential to become as important to cave-explorers as the Himalayas are to mountaineers.
     The scale of this place is almost incomprehensible until you visit. Vast is an understatement. Travel is measured not by distance but in hours, and once you turn off the Eyre Highway, one of only two roads that link the populous states of the east to Western Australia, you feel very remote.
     To venture into the outback, you need to be self-sufficient, well-prepared and careful. You have to take everything - spare wheels, fuel and, most importantly, water. There may be flooded passageways deep underground, but the water is saline and undrinkable.
     It seems bizarre to think that when you leave the surface world and set off into the enormous cave tunnels with all your dive gear, you also have to carry drinking water for the day.
     Nullarbor Plain is not for everyone. The psychological adjustments are daunting. The discomforts of physical remoteness, heat, dust and flies are compounded by inability to wash and lack of contact with the outside world.
     Invisible until you are only a few metres away, the Nullarbor is host to some incredible caves. Aborigines once used them for shelter from the extreme heat or other purposes, but few settlers ventured here. It is no tropical paradise, and there are no fabulous coral reefs.
     No one ventured into the flooded galleries until the early 1970s, but what a feast of exploration the early activists enjoyed!

Crows and swallows
The big entrances are spectacular. It is as if the bottom has dropped out of the world at these points. Weebubbie, in particular, is like some giant pit-like quarry. The walls are overhanging, of a rich orange-brown colour and bare of vegetation.
     These holes are not easy to access; even more difficult to exit. Crows and swallows may seek sanctuary in the depths, but for snakes or anything else, the caves often present an effective trap.
     Once you leave the glare of the sun, the caves are awesome. Weebubbie and Cocklebiddy are among the largest tunnels in the world, and they lead to enormous subterranean lakes.
     Sheer size and elemental darkness can induce a real sense of agoraphobia. This is another world in which strict control of the imagination is required.
     its a struggle to transport dive equipment 90m down to the water, but from the early 1970s it was clear that the scope for cave-divers was immense. By 1983, Cocklebiddy was already established as the longest cave dive in the world.
     In recent years the site may have relinquished top place but exploration has now extended the overall length to more than 5km. This massive tunnel is broken by two substantial dry chambers.
     The first kilometre under water leads to the Rockpile air chamber, and this is more than challenging for most visitors. Relatively few people have achieved this swim; far fewer have ventured beyond.
     The big entrances are spectacular.

Porterage downhill
My hosts are Paul Axton and Chris Edwards, two of the most respected cave-divers in Australia. I could not be in better hands as we set off into Murra El Elevyn, the perfect introduction to Nullarbor diving.
     The entrance is only a short distance from the Eyre Highway, and while its a stunningly beautiful hole in the Earths crust, the scale of the site is not overwhelming. Ladders and ingeniously devised hoisting facilities provide relatively easy access to the cave.
     The warm, reassuring glow of sun-baked rock quietly gives way to a cooler, boulder-strewn tunnel.
     Then its down, down, down, like Arne Saknussen on his mythical journey to the centre of the earth. Suddenly you reach the waters edge, and heavy gear can be off-loaded.
     So far its all been easy going; the porterage has been downhill. its best not to think of the return, when the same gear needs to be transported vertically 90m back to the surface. There follows a second journey to collect the rest of the kit, and the sweat rolls down your back.
     You live for the moment you will slide beneath the surface. 10,000 miles and days of travelling, frustration, hardship and gruelling fatigue are pushed aside. After years of imagining, I am here...
     The water is 18ÂC, and of such clarity as I have seen only a few times before, in the springs of south-eastern Australia, or perhaps certain Mexican cenotes.
     With perfect control, Paul hovers in midwater with his reel while securing a safe belay. Having dived these sites numerous times, he is composed and able to interpret my erratic gestures. Chris, as second flash man, makes allowance for us both. This is one hell of a place, but when youre with the right people, you know things will work!
     Hundreds of metres of cave are traversed at relatively shallow depth. We break out from normal-sized tunnels and a breathtaking expanse of bouldery terrain stretches far beyond the beams of our torches. This is the biggest tunnel I have ever seen, and I am conscious that it would be so easy to lose sight of that almost invisible dive line, but losing sense of direction here doesnt bear thinking about.
     On the face of it, the watery depths of Murra are as extensive and desolate as the surface world of the Nullarbor. There are no fish or visible life-forms of any kind. But this is a special wilderness; and I marvel at the shape and sculpting of rock tunnels. In places the passages are completely elliptical. In others, rock pendants drape as though fashioned for an exhibition in a gallery.
     There are large and small circular domes in the roof, where exhaled air gathers like pools of mercury, sparkling in the laser-like beams of our powerful HID lighting.
     Tommy Grahams may not sound like an inspired name for a cave, but it was to provide an even better dive. The hardships of the porterage are quickly forgotten as we cruise once more into an immense void.
     Everything about this stark inner space environment is captivating. The Nullarbor limestone is some 25 million years old, and here and there fossils of urchins and other shellfish can be seen either lying on the floor or standing proud, etched and eroded from the very rock in the cave wall. An hour later I emerge, feeling more impressed than on any other cave dive. Tommys was a magnificent recreational dive, on the international stage a world cave classic.
     Then its on to Weebubbie, a couple of hours drive east and requiring a change of campsite. They have kept the best till last.
     I wont go into the porterage. Once again the place is enormous, as big in the approach as Cocklebiddy. The lake, some 140m long, gives way abruptly to a steep boulder descent. Diving is often compared to the wonders of flight, and in my experience nowhere is this truer than in Weebubbie.
     As Chris and Pauls lighting punches into the vastness of the worlds largest underwater tunnel, it feels like a scene from Star Wars. The lads swim 10-20m apart to try to convey the scale. Fortunately the rock here is a creamy white, massively assisting penetration of our powerful strobes. We have several dives in Weebubbie; we flood flashguns and accidentally damage other equipment, but nothing can diminish the wonder of the place.
     Were sitting around the campfire on the final night. The last few beers are going down a treat. Sparks jump from the crude stone circle, meteorites speed to earth. Unlike many of the earliest British settlers, I have come voluntarily to the other side of the world to endure poisonous spiders and snakes, scorching heat, plagues of flies, and penetrating dust.
     By normal standards I would agree that this is self-imposed suffering bordering on masochism. But it was absolutely fantastic.

  • Hear and see more about Martyn Farrs Australian and other dive trips at the Dive 2005 show at the NEC in October.

  • Cocklebiddy
    Cocklebiddy Lake has been the site of world-record penetrations
    Weebubbie ; leaving the lake
    Using nets for protection from the flies
    Paul follows the line in Murra.