Although it was way back in nineteen eighty-nine, I have a clear memory of the events and because I have always had a bit of a writing bent, I had also been keeping detailed journal/diary, from an early age.

When the Heim story really started for me, I was a twelve-year-old boy having a most enjoyable childhood in Australia - the 'Lucky Country,' as we called it then.

I was with my best mate Huey. I knew he was my best mate because we were always arguing or criticising each other, and it sometimes came to blows. The fighting usually started when I called him a 'bluey' because of his ginger hair. He was a big, broad shouldered, tough bugger too. Still is. Although, belying his burly stature, Huey is quick witted and intelligent - sharp as a tack.

I remember that the weather was a bit weird for mid-summer in Western Australia. Hot, high cloud with brown stripes and also some low cloud that dumped occasional summer showers onto the parched scrub. I can still remember the smells and sounds on that day too; the smell of rain on dry earth and gum leaves and the screeching of the white Corellas, the pink and grey Galahs and the big black Carnaby Cockatoos, atop the pine trees. It was our Shangri-La.

We were at old Harry's place, up on the coastal strip about a hundred kilometres north of Perth, Western Australia's capital city. We were there with my dad - up to do a bit of fishing off the rocks on a nearby beach and to help Harry with maintaining his property. I'm not sure how my dad and Harry got to know each other, but they went back a long way. I think they served together in the Australian Army although Harry was quite a few years older than dad. I seem to recall dad saying that he was an NCO in the unit where he did his National Service in Vietnam. That was over five years before I was born, and they never spoke about it when I was around. I was told that he was my godfather, and that he would look after me if anything happened to dad. Mum shot through a few years back and I don't know where she is, so I only had dad. I didn't think I'd ever need Harry, but I was polite to him just in case.

My recollection of old Harry was that he was, what I would now call, a private person. Not shy - forthright, a bit reticent and a bit stubborn. He was very patient with us kids though. To me he seemed well-read, intelligent and extremely knowledgeable on a wide variety of subjects. He was a big, tough, man with a weathered face and a bushy grey beard. To us he was 'old' but in fact he was probably in his mid-fifties - making him about seventeen years older than my dad.

The place was a bit run down and dad and I helped him to fix up the fencing and sheds. It was about forty acres of land with some paddocks with Merino sheep and a couple of goats. The rest was bush, with grass trees, banksias, low scrub and a row of conifers he'd planted aside the house as a wind break. It was uneven land with lots of hillocks and limestone outcroppings. It wasn't particularly good land.

Huey and I camped out in a paddock at the back of the homestead whilst the 'oldies' stayed in the house. We had been coming up in the summer for a few years, were used to the bush and knew how to avoid snakes and red-back spiders. We were allowed to roam freely all day and sometimes half the night.

That day we'd ridden our old bikes down to the beach to do a bit of fishing. We didn't catch anything and I could see Huey was getting bored. He got bored easily. He nagged me into going back to the property to go on an exploratory hike to see if we could find the caves that old Harry had mentioned over dinner a few nights earlier. I didn't fancy the weather but I tagged along anyway, because the alternative was to help old Harry to pull fence wire, and I was sick of that.

We had heard dad and Harry talking about deep caves that the previous owner had sworn were out there, somewhere under the limestone rocks in the far paddocks, but Harry said he wasn't sure if they were there at all. He'd never seen them.

We made ourselves a packed lunch, got a couple of bottles of water, a torch and set off for a day's adventure. After a 20-minute walk and a few false starts we found a couple of caves - but these weren't very large or deep. The former owner had told Harry about a deep cave, with a kind of shaft that went down a fair way. He'd said that the entrance was small but when you threw stones in it seemed a while before they hit bottom. Harry reckoned that, if it was there, it must be at the back of the hill - near the top. We decided to look for it.

After another half hour of fruitless searching, we stopped and sat under a small tree in a clearing in the bushland to eat our lunch.

While we were sitting there, trying to keep the flies of our sandwiches, Huey squinted up at the rocks and said he thought he could see a vertical slit behind a rocky outcrop. We had already searched that area but were looking down for holes in the ground and watching where we put our feet. If it was a cave, we had probably walked right past it, thinking it was a shadow on the rocks. It must have been that the sun had moved around revealing the fissure. We remembered that Harry had been told that there definitely was a deep cave, and he seemed to believe it, so we decided to climb back up and investigate what Huey had seen.

It was a cave alright - and a deep one at that, by the sound of the stones we tossed in - but the entrance was very small. I had a smaller build than Huey but the entrance was too small even for me. We shone the torch in and, from what we could see, the cave seemed to widen a bit inside, go horizontally for a short way and end up in what looked like a dark hole. One side of the entrance seemed to be fairly loose rock but we couldn't shift enough to get in. We decided to come back tomorrow with hammers, chisels and a couple of wrecking bars and some rope.

That night, around the barbecue, we talked about what we had found and what we intended to do. We asked Harry for a rope and tools. He said that it seemed like a good plan but that there might be a few problems; firstly, clearing away rocks to make the hole bigger might cause a cave-in, so we would need some way of propping up the roof. Then, he said, if we did get in and go down the hole on a rope, we may get stuck, or cause a rock fall, or fray the rope, or run out of rope. Also, he pointed out the problem of making the entrance safe so that other people, sheep or goats wouldn't fall into the hole. He reckoned that for any expedition you need to make proper plans and preparations, get the right equipment and anticipate as many problems as you can. Dad told us to eat up and said that we would talk about it again tomorrow - obviously hoping that the thought of planning and preparing would dampen our enthusiasm.

It didn't dampen Huey's. He wanted to talk about it as soon as we got up. Dad didn't seem too enthusiastic but Harry seemed quite keen to go and have a look himself. He said he had done a bit of climbing when he was younger and still had some of the gear. He reckoned that it would be okay to use for potholing. He said that first we would all drive up to the cave, in the Ute, and see if we could to make the hole bigger.

We put mallets, chisels, a sledgehammer, assorted timber, stakes and chicken wire in the back of Harry's Ute and he drove us up to the hill where the hole was.

It turned out to be quite easy to enlarge the entrance so, after shoring up the roof with timber, we broke away enough rock to allow us to crawl in. Inside, the cave was wide enough for us to all stand in and look down the hole. Harry shone a torch down and said he thought he could see the bottom, but it was a fair way down. He said that the hole was quite wide for most of the way, but it narrowed a lot about three quarters of the way down. He said we should go home for some lunch and, as we were going home the day after tomorrow and the weather might change, we would come back later in the day, with some climbing gear, and give it a go. Before leaving he hammered two steel star pickets in the ground outside the cave entrance and secured some chicken wire across to keep the animals out.

After lunch Harry dusted off and checked out his climbing gear and selected a few items - helmets with lights, lanterns, climber's shoes, gloves, two static ropes, two harnesses and some descenders and ascenders.

Back in the cave, he lowered the lantern on the rope and had a good look at the hole. He decided to go down and have a look but said he wouldn't be able to go past the narrow bit. He secured the rope to a nearby rocky outcrop, put on his gear and went down into the hole. He said that there were some interesting formations and a couple of fissures that may lead into horizontal caves. After about ten minutes he returned to the lip of the hole. He said that he had been down as far as the narrow bit and it seemed quite safe. No loose rocks. He said the narrow bit was a bit tight for him, so he didn't to risk it.

We packed up for the day and went back to the house, planning to make another attempt the next day, our final day there, weather permitting.

I still remember that day all so clearly, like it was yesterday. It was fine, but hot and windy. We had returned with a pipe frame rig to secure climbing lines and a block and tackle pulley to lower gear down or bring any interesting rocks up. We also had one of old Harry's Russian cameras, with a flash attachment, and two powerful battery-operated spotlights.

We shifted the chicken wire and all went into the upper chamber; glad to be out of the wind and heat. I recall that it was quite cool in there with a breeze coming up from somewhere below. The cave was just big enough for us and the gear. We could stand up, which made it fairly easy for us to rig up the frame; two tripods embedded in rock cavities and a cross bar - secured with scaffolding fittings. Harry tightened it all up and pronounced himself satisfied. It looked pretty sturdy to me, but then old Harry always did things thoroughly. I learned a lot from him as a boy. After that, he rigged up the block and tackle and hooked a metal bucket on the end of the rope.

We lowered the bucket down first with the camera and a spotlight in it. We lowered it to a ledge where the hole narrowed and Harry tied it off securely. He said he would rope up and climb down first while we shone the other spot down and watched carefully what he did. He said, if it was safe, Huey or I could go down after him.

Harry's climb down seemed pretty easy, although I remember him muttering and cursing all the way down. I hate to think what he would have said had there been any real problems. He said that the walls still looked safe enough - no danger of a rockslide. Trying to squeeze through the opening into the lower chamber he almost got stuck. Then the cursing really started, and Huey and I learned a few new words.

After finally extracting himself, he had a good look down into the lower chamber. He said it widened out again and dropped down about three metres below him to a relatively flat floor. He muttered something about interesting formations and a dark spot which he thought might be a side passage. He sounded pretty annoyed that he couldn't go down further.

"Okay", he said. "One of you young skinny bastards will have to come down and take a look". Huey and I both wanted to go so we argued for a few minutes. Harry and dad finally lost patience and said we could both go, but one at a time. Then we argued about who should go first - until dad shut us up and decided for us. He said that, as I was thinner and lighter than Huey, I should go first.

Dad wanted to tie me up and lower me but I'd watched Harry go down and I had a pretty good idea how abseil down the wall, so they let me do it my way. It wasn't far down but it was fun.

There was plenty of room for two, but not enough for three, so Huey had to wait up top until I had climbed back up. More whingeing. Harry was busy taking photos of the rock formations and of me coming down. When I got down to him, he gave me a quick lesson on how to use his old camera. He said the aperture and timer were set up and that I just had to click and move the film on. He put the camera and spotlight back into the bucket and called to Dad to lower it to the bottom of the second chamber.

After commenting on my clumsy descent, and giving me a few tips, he let me go through the narrow opening and climb down into the lower chamber.

At the bottom, I shone the spotlight all around the walls and floor. Harry was right, there was a passage off the chamber, but it didn't go very far in because it was blocked by an interesting formation; a piece of flat rock, partly covered by stalagmites and stalactites. It didn't look like limestone - more like grey metal or plastic. I stepped in to take a closer look. When I touched it, it didn't seem as cold as the surrounding rocks. There seemed to be a current of damp air coming from a hole at one side of the passage.

I described it as best I could to Harry and he told me to take a few photos, making sure that the flash was on. I took three pictures. On the third flash I heard a sort of high-pitched whine coming from the cave. It scared the crap out of me, so I ducked out of the passage, chucked the camera and spot into the basket, grabbed my rope and scrambled back up to where Harry was waiting.

I recall that I was shaking like a leaf when I got back through the gap and I was yelling to Harry to get us back up and out of the bloody cave because there was a bomb down there. He tried to calm me down, but I wasn't having any of it. I just climbed up to the top chamber and out of the cave as fast as I could.

By the time I had plucked up courage to go back in Harry was back up and they were packing up the gear.

On the way back to the house Huey gave me a hard time, making chicken noises all the way back. He was pissed off because he hadn't been down the cave himself. Harry was pointing out that it could hardly be an unexploded bomb as it would have taken many thousand years for the stalactites to form and that the noise was probably wind blowing in from another cave entrance somewhere. Anyway, he said, the photos might tell us something.

Harry was a bit of an amateur photographer, had his own little darkroom and developed his own pictures. He went in to develop the roll of film as soon as we had stowed the gear and had a cup of tea.

Later that evening, after dinner, he brought out the prints for us to see. Most of them were pretty boring shots of rock formations and me abseiling down the cave wall but he seemed very interested in the last three; my shots of the passage. He studied them intently with a magnifying glass for a long time before mumbling something incomprehensible.

He said he thought he could see what looked like dots and parallel lines on the smooth section of the rock blocking the passage. He said they must be aboriginal cave drawings but he'd never seen any quite like that; so deep underground and apparently etched into the rock, and so straight and regular. He said that all the other rock art he'd seen was painted or mouth sprayed with pigment, but he could be wrong.

I asked if we should tell someone. Perhaps a university or museum. After much thought and discussion, he decided to do nothing - just block up the cave entrance and keep quiet. He said he didn't want his peace disturbed by people crawling all over his property. He said there was plenty of other aboriginal cave art around and he didn't want the aboriginal people declaring it a sacred site. He said "let sleeping dogs lie, and that's an end to it". He put the photos in a drawer in his desk, changed the subject and wouldn't talk about it anymore after that.

I sat up late that night and wrote everything that had happened that day into my old battered notebook. I had a strong intuition that this wasn't the end of the mystery. I could not have then imagined how fortuitous Harry's decision to keep quiet about the find would turn out to be. Revealing it then would have, literally, changed world history - and probably not for the better.

The next day we went home, and I never saw old Harry again.