IN SEPTEMBER 1982, three Australian cave-divers surfaced after an almost-4km underwater swim in Cocklebiddy Cave to a huge underground lake and a series of dry rock chambers, the like of which had never been seen in Australia.
Ten metres high and 250m long, their discovery was given the name Toad Hall. Why they called it this is a secret they preserved. Cocklebiddy was recognised as the longest submerged cave passage in the world, and though this record has long been surpassed,
a swim to Toad Hall is still regarded as a long-distance cave penetration.
As Hugh Morrison, Ron Allum and Peter Rogers had done 27 years before, I emerged into Toad Hall after a spectacular underwater journey.
I was excited to have made it this far on my first Australian cave dive, and equally excited to find out how this place had got its name.
My dive partner Agnes Milowka, from Melbourne, had been born the year Toad Hall was discovered.
We removed our dive gear, scrambled out of the water and climbed into the dry chambers to find a plastic slate bearing many names. All those who make the journey have the honour of adding their name to what is a whos who of southern-hemisphere cave-explorers. Fewer than 50 people, and only one woman, had signed the slate.
We added our own names and, despite the high levels of CO2, moved on to explore Toad Hall for ourselves.
At its far end, the cave once again breaks down and, in typical Cocklebiddy fashion, a pile of rocks leads down to yet another sump, or submerged passage.
Three days later, Agnes would dive almost the entire swimmable length of this sump, claiming an Australian record for the furthest underwater cave penetration by a female diver.
After exploring Toad Hall, we spent two more hours photographing the various chambers. With more photography on the way back, and a round trip of almost 8km, mostly under water, we finally emerged into the entrance lake 14 hours later.
Whats more, a small scooter malfunction had required Agnes to swim 2.5km of the distance - nothing she hadnt done before, she assured me.
Yet our photography trip into Toad Hall felt insignificant compared to the full-on assaults on sump 3 that were being set up around us.
This March 2009 expedition was an extension of attempts by the same team the year before to find the true end of this submerged cave.
Lead divers were Australians Dr Craig Challen and Dr Richard Harris, and Rick Stanton, who had travelled from the UK with me. A highly experienced team of divers would support the venture.
Our camp was pitched in the heat of the Nullarbor Plain desert, which covers an area of about 77,200sq miles. It stretches about 750 miles east-west between South and Western Australia at its widest point.
In daytime, temperatures can reach 48°C. Night brings freezing conditions, and creatures that make you wonder where they live by day. The flat, featureless Nullarbor is home to thousands of kangaroos and the odd deadly spider, so protecting your tent is a high priority. But as the largest single piece of limestone in the world, Nullarbor is a Mecca for cave-divers, and Cocklebiddy is the largest and longest known cave in Australia.
The 14 of us were camped just outside the cave entrance. Out here there is no water, no showers or toilets - everything has to be brought in.
Massive generators towed out to the desert powered the camp and the powerful lighting being run into the cave - not to mention, in typical Aussie fashion, fridges to cool the beer!
Tons of diving equipment had to be lowered into the cave using an A-frame, then manhandled down to the huge underground lake that marked the start of diving operations, 90m below the camp. This meant heaving equipment down a boulder pile over a distance of 200m in the dark.
Safety cylinders had to be dropped strategically along the cave in sump 2,
to be available while transporting the equipment required for dives beyond Toad Hall, and on the dives themselves. This took several days.
Cocklebiddy consists of three dives. Sump 1 is 1.2km long, and runs from the lake to the first air chamber, the Rockpile. Divers must then remove all equipment and carry it over 100m of collapsed rocks before continuing to the magnificent, 2.5km-long sump 2.
Once at Toad Hall, divers once again have to carry all their gear 220m to sump 3, which is about 1.7km long in explored distance. About 1.2km of this is reasonably big, then it becomes a lot smaller, though still swimmable.
At about 1.5km, the passage becomes too tight to swim through with a back-mounted system. Side-mounts can be used for the next 100m or so, before the passage becomes even smaller and requires a no-mount approach, divers pushing whatever it is they are breathing from ahead of them.
If you have reached this point, 5.7km into the cave, chances are you are not using conventional scuba.
The push-divers on this expedition were using variations of their own home-made rebreather configurations, considerably smaller than standard manufactured units.
Each was appropriately named for the environment in which it was being used. Ill leave the names to your imagination!
The Cocklebiddy entrance is the result of a surface collapse at one point in the caves length where, 10 million years ago, it became too large to support the rock above. The existence of a southern passage has been suggested, but until someone finds a way into it, divers concentrate on exploration upstream.
There may be other caves under the Nullarbor that are even bigger, but of which we are unaware. The fresh water that permeates the limestone meets existing salt water underground, and the corrosive action dissolves the limestone to create the cave.
Rick Stanton had to think about it overnight, but after his first dive in sump 2, he declared it the best sump he had ever dived. The passage is unlike the other two, in that it is large enough to drive two double-decker buses through side by side.
As it winds, your scooter pulls you through a beautifully decorated passage of calcite and white flowstone in crystal visibility. The more powerful your torch, the more amazing your experience!
This was one of the best dives Ive done. Looking back now, I almost doubt that the experience was real!

THE FIRST DIVE IN COCKLEBIDDY took place in 1961, though lack of gear prevented the divers from penetrating any distance into the submerged tunnel.
The first serious dives occurred in the early 1970s, when several hundred metres of line were laid.
In the mid-70s, a joint South Australian team pushed the cave distance to 1.5km to discover the Rockpile, a long lake with a 20m-high roof and an 80m-long heap of rocks. Beyond it, the divers discovered sump 2.
Most years of the 70s after this saw further explorations of sump 2. The submerged passage grew longer, divers pushing ahead of them sleds of multiple cylinders.
In 1983, a year after Toad Hall was discovered, five French cave-explorers headed by brothers Frances and Eric Le Guen set a new world record for underwater penetration.
Eric did the first dive and managed a 1460m penetration into the third sump. Frances later managed to push the cave another 90m by squeezing through a restriction, but was stopped by a second restriction too tight for him to negotiate with his back-mounted tanks.
The brothers broke the entrance lake surface of the first sump 47 hours after their departure on the second dive.
Soon after the French left, Australian divers took back what they felt was rightfully theirs, and other leading-edge divers continued to push forward.
In 2008 Craig Challen laid an additional 100m of line from his predecessor Chris Browns reel, and found himself in a very low bedding plain, against the flow of water in near-zero visibility. He was forced to retreat by low gas levels.
The plan was now for him and fellow expedition-leader Richard Harris, an Adelaide-based technical diver who holds the Australian and New Zealand record for the deepest dive, to make separate attempts on different days, before well-known UK cave-diver Rick Stanton had a go. There would be room for only one man at a time down there!
The key to success would be use of closed-circuit rebreathers and diver propulsion vehicles. Another Australian team-member, John Dalla-Zuanna, had developed lithium-battery power for the DPVs sufficient to transport the men to the far reaches of the cave and back. This would save an 11.5km swim.
Unfortunately, equipment problems meant that neither Craig nor Richard was able to reach the end of Challens 2008 line. Disappointed, all they could do was wait to hear how Rick Stanton would get on.
I planned to see Rick safely off from the lake and, later that night, meet him at the Rockpile. I would be the only person he would see underground. From the Rockpile I could contact the surface, using a cave radio system, to let the team know when Rick arrived back safely.
Having reached the end of Craig Challens line, Rick tied his own off to the end of it. From here, he progressed only a few metres. The cave was now a wide bedding plain some 20-30m wide, big enough for a diver to negotiate only by passing through rock-erosion features and channels in the floor.
Rick had little if anything to which to belay his line, and had to move elbow-deep in mud, in zero visibility. Cocklebiddy is a percolation cave, so the point reached by Craig in 2008 could well be the source of the water.

RICK REELED IN THE FEW METRES of line he had run out and retreated, claiming that there was no more passage to be found, and that Craig Challen had officially reached the most remote part of the cave the year before.
At this point in the cave there is little possibility of it opening up again, and it will certainly become too small for a human to progress far beyond.
I had waited in darkness for five hours, contacting base hourly. Just as a storm was passing through the camp above, the powerful lights of Ricks torches appeared, and I helped him carry his gear over the rocks to sump 1. We dived out a few hours later.
Our expedition was over. We had taken 11 people to Toad Hall, the most at one time, and the first two female divers had reached sump 3, one setting a new distance record. We also had a clear understanding of the geology beyond Toad Hall.
And the name Toad Hall Sorry, youll have to go and find out for yourself!
But remember, to dive in Cocklebiddy Cave you must be a penetration-qualified cave-diver. Apply for permits to the CDAA (Cave Divers Association of Australia),