When Hong Kong business executives worry that their firm might collapse if they take a two-week holiday, they should think about Andy Eavis. The 50-year-old Briton set up a plastics moulding company about 15 years ago. It now employs 300 people and turns over about GBP20 million (about HK$264 million) a year. But Mr Eavis is often absent. While his employees make widgets, he is exploring enormous holes in the ground. He is, in fact, one of the world's foremost cavers: and he spends much of his time in caverns in Southeast Asia, and increasingly in China. 'That [the plastics firm] brings in the money; that's my proper job,' he said during a visit to Hong Kong this week to speak on his exploits to the Royal Geographical Society Hong Kong. '[But] we brought in a managing director a few years ago, so now I'm in a position to take time off.' He has used that time to pursue his 'improper' job - finding and exploring some of the world's biggest and deepest caves. He does it, as mountaineers would say, because they're there - but as yet unseen by many people. 'If it was 300 years ago I'd probably be sailing and exploring countries, but there are none left to explore. I like exploring, and I'm at home in caves; I think they are friendly places. 'I guess I have been responsible for [opening] about 640 kilometres of cave passage. Many of them are 100 metres wide, so I've explored the equivalent of a small country.' He stresses that we are talking big. Forget the image of someone crawling through narrow tunnels or gasping claustrophobically in some airless hole just big enough to stand in. He tries with increasing animation to get across the grandeur, the awesome beauty of dripping crystals and clear blue-green lakes - and most of all, the enormity of the spaces and the experience of finding them. 'Some caves are so big you get clouds forming inside. You get underground rain,' he said. 'When you are in something where you can't see the walls and the ceiling, I've had more trouble with people getting agoraphobia than claustrophobia. It's difficult to give people an idea of the scale when if you take a picture of a person against the wall, to show the size, you can't see the person . . . You can fly planes in, turn them around and fly them out again. 'We are exploring new caves 200 feet [60 metres] wide, bigger than the biggest motorway. If I've got to stoop or turn sideways, I don't bother.' Reaching them does not always mean descending, either. Many of these caverns are found in limestone towers such as those that rise above the Guilin landscape, meaning a climb to the mouth followed by a drop into their heart. He became interested as a youngster in Southwest England, near the cavern-riddled Mendip Hills, but desisted from exploring for the sake of his worried parents. He was able to satisfy his curiosity once he got to university, and particularly when during his second degree in mining engineering he joined one of the world's best caving clubs at Leeds. An expedition to study glaciology in Norway got his name known to other cavers. After that, he was invited to join a Papua New Guinea trip as a 23-year-old 'lad'. He ended up running it - 'making every mistake possible', he says now. He joined Britain's National Coal Board in the 1970s as a mining engineer, where he 'fiddled the holidays so much they had to change the rules after me'. 'I managed to get 10 months in Papua New Guinea, most of it paid. Or I had three months in Borneo, all of that paid.' That Borneo trip, to Sarawak in 1978, was very successful. The organisers, the Royal Geographical Society only added caving at the last moment. The aim was to set up a national park to protect the rainforest in Mulu but 'they discovered there were caves there, so they looked on their list for cavers and I was there. 'We immediately discovered the largest cave passage in the world - about 50 kilometres long. I remember sitting down pinching myself to see if I was really there.' When they were able to return and map the cave properly, they measured it as 200 metres by 200 metres and a kilometre long. On each of two subsequent trips, in 1980 and 1984, his group found another 50km of passages - and stumbled into what turned out to be the biggest chamber in the world, an enormous vault where they could only keep their bearings by leaving a mark where they started and following one wall around until one member complained of agoraphobia. A later survey measured it at about 700 metres high and 400 metres across, part of a vast cavern chamber system that would hold three Wembley stadiums. Having done the biggest, he turned his attention to the deepest, and that has brought him deeper into China. The vast limestone deposits on the mainland dwarf those elsewhere. China is thought to hold about half the world's caves, and with large areas of the rock in Vietnam, Laos, Cambodia and Thailand, Southeast Asia comprises the world's most extensive tunnel systems, he says. While easily accessible caves had been found and searched by locals, 'long, deep, wet, difficult caves [are] the preserve of sport cavers, who produce the maps which become the basis of any cave studies,' says a 1989 report from the British Cave Research Association. While China was virtually closed to outsiders, cavers could only 'look eastward and dream,' the association wrote. Then in 1982 Mr Eavis and others were allowed to do a first reconnaissance trip and set up contacts that have grown into the China Caves Project, a loose association between British and Chinese academic explorers in Guilin, Guizhou and more recently, Sichuan. Some are nearly 1,000 metres down and 'very, very spectacular', the association says. Finding where the best caves are employs a mixture of simple geological knowledge, experience, modern equipment and sometimes using one's wits. Most caverns have been formed near the equator, where humidity, heat and high carbon dioxide levels from rich rainforest areas formed ideal acidic atmospheres to eat away the chalk that itself had mostly formed from corals growing in those areas. Now, he says, continental drift over thousands or millions of years has carried caves to other interesting sites such as Tierra del Fuego at the tip of South America. Even simple maps can show up interesting places: 'I've got a map that shows the whole of China, and you can see rivers that just stop, and further along they start again. Where they disappear, there'll be a cave.' Satellite or aerial photographs, looked at with a stereoscopic viewer, can show them up. And then there are the cavers who use other people's work to jump in themselves. 'It is quite competitive,' he says. As president of the European Caving Association and vice-president of the World Caving Association, Mr Eavis tries to keep people to 'their own areas' but it doesn't always work: 'We arrived in Sichuan Province once to find a full-blown French team already there, staying in the same hotel. In the end they went to another area, but it wasn't good form, they should have checked with us.' There are all sorts of discoveries to be made, from huge tadpoles that fill a human palm but never turn into frogs, to cave paintings in Sarawak. Despite the caves' obvious potential as homes or Jesse James-style bandit hideouts, Mr Eavis' biggest disappointment so far has been his failure to find signs of human habitation - though he has discovered the bones of explorers who obviously could not find their way out. Yet caving is not just a fun pastime. He has helped the Chinese and Javanese authorities map caves that have since been turned into tourist attractions or, more importantly, water sources for arid areas. 'Limestone does tend to be dry because the water disappears underground. In China for the next three months there will be areas where they are desperately short of water. We can find underground lakes that can at a stroke solve the water problem for a village. Sometimes local people have stopped him entering caves to prevent him disturbing spirits. But he has survived other, more immediate dangers. An earthquake rumbled along a tunnel like an express train passing him; he has had boulders drop on him and just avoided the venomous spit of a king cobra by leaping over it for a rope hanging above its head. Abseiling into a shaft in Java, he ran out of rope unexpectedly and had to sling a clip fast on to the taut life-line to prevent himself falling 15 metres on to boulders - later he discovered that 'the locals had been tidy and untied the ropes from each other'. 'I'm on my ninth life; I've been a lucky man.' Badly-looked-after tourist caves where stalactites are broken off for sale, or ruined areas such as the now disastrously over-logged Mulu, depress him, he says. But his team tries to avoid that by helping to set up protective management and convince people of the merits of conservation. So how long can he continue? He remembers returning from a wet, cold, unsuccessful trip to China last winter, struggling through tunnels of rushing wild water and gaining several months' pain in his knees for his trouble. Yet he plans to return next year - 'in summer, thank God' - to explore a gorge that has been described as one wonder of the world: about 10 metres wide, 200 metres deep and more than 1km long. And he has just returned from a reconnaissance of unexplored caverns in Sichuan 'with a river the size of the Thames running through a cave that no Westerners have been to before'. That is what keeps him going. 'Chris Bonington is still climbing mountains at 60-odd, and if he can climb mountains, I can explore caves.'