Last night my boyfriend's testicles were attacked by biting ants,' reads one comment in the guestbook at Khao Sok Rainforest Resort. Another remarks on a bird-eating spider discovered in a bathroom. More happily, greater numbers of people mention 'the flower'. The largest national park in southern Thailand, Khao Sok is one of the country's finest natural assets. Connected to a series of other parks, and covering 738sqkm, it makes up part of the largest area of preserved forest in Thailand and is the last natural haven in the south for wild elephants and tigers. Its prize possession, however, is what many here simply call 'the flower'. Blooming to a diameter of about a metre, the rafflesia is the world's largest flower. Found in several parts of Southeast Asia, in Thailand it grows only in Khao Sok and the adjoining Khlong Naka Wildlife Sanctuary. Adding to its mystique, the endangered rafflesia blooms for just three days a year. A parasite with no roots or leaves, it exists for most of the year as microscopic threads growing inside the roots of trees. Buds swell to the size of footballs then burst open in January or February, revealing petals like the blades of a boat propeller. Three days later, it shrivels to black pulp. Visiting Khao Sok primarily to see this floral wonder, the news is initially discouraging. 'There are none in flower - only buds,' says a ranger at the park visitor centre. From the centre, two walking trails radiate into the park. The main trail follows the Sok River past a series of waterfalls to Ton Kloi falls. Midway, the path is crossed by a tributary along which a rafflesia was found in 1994. Following the discovery, an Exotic Species walking trail was created from the main track into the area around the rafflesia. The trail was later abandoned and left to grow over, but I hope to find traces of it along the Sok River. Two things quickly become apparent. One: most waterfalls here are little more than glorified rapids. Two: finding a way along the tributary will be next to impossible. This jungle devours unused trails at a furious rate. The only thing to do now is wait and hope that somewhere in the next few days a rafflesia will bloom. In the meantime, there's plenty to do. Travel agencies along the park entrance road offer a range of carbon-copy trips into the park, from night safaris to elephant trekking, river tubing and guided walks along the Sok River trail. I opt for Cheow Lan Lake. Covering 165sqkm, Cheow Lan was created with the construction of a dam in 1982, two years after the establishment of the national park. It's become Khao Sok's centrepiece, with limestone cliffs rising hundreds of metres from its shores. Rather fancifully, it's been likened to China's famous Guilin landscape. I travel to the lake with local guide Bee, who grew up wandering the jungle with his uncle. Bee has seen wild elephants, tapirs, even two panthers, he says, but never a tiger, supporting the suspicion that few of the big cats still exist in the park. 'The old people say there are seven tigers,' Bee says as we climb aboard a long-tailed boat. For 90 minutes we skim across Cheow Lan, passing beneath a saw-tooth line of peaks. Between bare cliffs weathered into wax-like shapes, rainforest thrives in the narrow gullies. We stop for lunch at a line of raft houses, a colourful kingfisher the only other guest, before continuing up a narrow arm of the lake overhung with jungle. That we will trek here seems improbable. The skipper stops the boat and Bee steps ashore, his arms spreads wide. 'Welcome to the jungle,' he announces, and then clips away in his flip-flops into a forest buzzing with life: buffalo spiders complete with horns; gangly stick insects that resemble balloon animals; butterflies as big as sparrows, but with wings like rice paper. We walk for two hours to the wide mouth of Namtok Cave, burrowed into a range of limestone hills. Through the cave's damp darkness, we splash past mound-like stalagmites that resemble waves about to break. Bats crowd the ceiling, catfish swim about our feet and tiger spiders as big as my hand cling to the walls. As the wide chamber narrows to a slot, the gentle water flow turns to rapids. Twice we plunge into deep pools, swimming a few metres back to shallow water until sunlight again pours into the cave. We step back out into the jungle, following the siren-like song of gibbons back towards the boat. When I return to my lodge late in the day, the owner greets me with a knowing grin. 'The flower is in bloom,' she says. 'We take you to it after breakfast tomorrow.' I'm woken hours before dawn by an impatient rooster, but still we leave the lodge an hour late. With a flower that blooms so briefly I'm worried that the delay will be critical. Is it shrivelling, even as I sit waiting for Ball, my new guide? After Ball arrives we drive for 20 minutes, stopping in a grove of rubber trees, from where we begin walking. The relentless climb is punctuated by Ball's staccato interpretations: 'Jackfruit'; 'Chameleon'; 'Bamboo'. Staring into the canopy, Ball is so intent on decoding the jungle for me that he doesn't see the snake. When he steps on it, the snake shoots out behind him, too quickly for me to react. I watch horrified as it slides between my legs. Overhead, we hear the call of a hornbill, a toucan-like bird I'd almost give up the rafflesia to see, although it's hidden better than the many chameleons on the tree trunks around us. After an hour we start to descend steeply to a small stream. A few steps up the opposite bank, Ball barks out one last name - 'Flower' - and we're here. The throne room of the floral world. Although it's small by rafflesia standards - about 60cm across - the flower is still bigger than I imagined, looking like a giant hole with wings. Its dry mulberry-coloured skin suggests that it's already old. By tomorrow it may be gone. Sprinkled around it are dozens of buds, looking like brown cabbages, ready to take its place. Ball wanders on, and I hear an exclamation of pleasure above me. 'Up here, big one!' he calls, suddenly talkative. Among a blackened graveyard of shrivelled rafflesias sits a new flower. Its fleshy petals are still opening as though we've caught it halfway through a yawn. Inside, its stamens resemble the arms of a sea anemone. I sit beside the flower and feel myself shrink to gnomish proportions, suddenly tiny in a large jungle. Overhead, a hornbill chatters in the tree tops, but I'm too distracted to care. Getting there Dragonair ( www.dragonair.com ) flies from Hong Kong to Phuket, from where Khao Sok National Park is two hours by bus. There's a wide selection of accommodation in the village that lines the park entrance road. Khao Sok Rainforest Resort (krabidir.com/khaosokrainforest) and Art's River View Lodge (krabidir.com/artsriverviewlodge) offer tree-house accommodation.