Hiking in one of the most crowded places in the world? It sounds bonkers but, as Carole Cadwalladr discovers, minutes from the city's cocktail bars, there are spectacular peaks to climb, idyllic beaches to surf, coral reefs to snorkel

Who needs a rucksack to go hiking when you can take a wheelie case? As well as strappy sandals, a summer dress, a Time Out city guide, a big fat novel, various hair products and unguents, and there, buried at the bottom of my case like an afterthought, a pair of stout walking boots, and a sensible fleece.

When I finished packing it struck me that it looked like the kind of case Bear Grylls might pack if Bear Grylls were a tranny, but then I was going on the most surreal hiking holiday known to man, in one of the most densely populated cities on earth, and, frankly, luggage was really the least of my issues.

I was, in fact, going hiking in Hong Kong, which sounds like one of those oxymorons made up by an overenthusiastic tourist board, like a Dubai culture break or a Scottish winter sun holiday, with the crucial difference that you actually can go hiking in Hong Kong. No. Really. Proper, in the middle of nowhere, slogging your guts out up a mountain trail, hiking. It surprises a lot of people who haven't been to Hong Kong but then again it also surprises a lot of people who have. I went pre-handover and had no idea it was anything but high-rises until my friends Aussie Pete and Czech Zuzana, who live there, rang up and invited me camping.

"Camping? Are you mad?" I said. But then I rang the tourist board and they said, oh yes, as if it were the most normal thing in the world, and found me a guide and a really spiffing hotel, the Mandarin Oriental, which, while not a tent - in that it had a marble bathroom as well as walls, a roof, a bed, liveried doormen etc - was, I decided, tent-like enough. For all I knew, Pete's idea of "camping" could easily involve sleeping rough on a Kowloon pavement.

There was a snag, though. Usually on a walking holiday, I end up in an Alpine hut sharing a room with four snoring Germans, the plus side of which is that when you put on your three-quarter-length trousers and your microfibre top, your thick socks and your stout boots, you don't have to walk past breakfasting businessmen and liveried doormen. I think I may have looked somewhat unusual.

Since Pete and Zuzana were working for the first part of the week, I was going to go walking in the day and then meet up with them for a spot of big city entertainment, and the tourist board had rustled up a walking guide called Fred.

Fred wasn't quite a walking guide, it turned out, so much as a guide, who appeared to have been cajoled into doing some walking. What do you normally do with your tourists, Fred? I asked. "Shopping. Always shopping. Sightseeing. Eating. But mostly people come here to shop." Not walking then? "Oh no!"

We were starting off with the Dragon's Back trail, a gentle warm-up on Hong Kong island, about a 20-minute cab ride away. I really couldn't believe that a 20-minute cab-ride could take you anywhere remotely wild, but by the time we had climbed to the first viewpoint, it was spectacular: undulating hills covered with thick vegetation, a series of beautiful bays, and not a soul to be seen.

It's the best urban hike in the world, according to Time magazine, although apart from a distant tower or two, and a couple of far-off villages, it didn't feel very urban at all. Over the top of the hill was the throbbing metropolis, the gorgeous shimmering Bank of China tower designed by IM Pei, and Norman Foster's HSBC tower, then the as-yet-unfinished International Finance Centre, which Batman jumps off in The Dark Knight. But on this side, butterflies fluttered in the breeze, and the sea shimmered in the distance.

"What's that building on the cliff top over there?" I asked Fred, thinking it must be some millionaire's pad. "That," said Fred, "is a prison."

There was something else bothering me. Where was everybody? "They are working. Maybe some come at the weekend but Hong Kong people are very lazy. Take me. On Sunday, I sleep until maybe one o'clock and then I go and see my family and eat a very big lunch."

The amazing thing about Hong Kong is that it is both one of the most populated cities in the world, and one of the least populated countries ... well, not a country, a "territory", but you know what I mean. Everybody lives in tiny flats in soaring skyscrapers but only some 30% of the land is built on. Because of Britain's world-leading position in petty bureaucratic planning rules - and here feel your patriotic heart swell with pride - the other 70% is countryside, most of it protected national park.

Parts of it are nothing less than breathtaking. The next day, I went out into the Sai Kung national park in the New Territories with an outfit called Kayak and Hike, set up by an Australian called Paul Etherington, and couldn't believe that I wasn't in Thailand or back a hundred years in time - give or take the fact that we were in an ex-police powerboat of the type that tends to get blown up in Bond films. We zoomed out into the South China Sea, past tiny wooden boats containing fishermen wearing conical bamboo hats of the type I've only ever seen in blatant racist stereotyping, past towering sea-cliffs and circling sea-eagles and postcard-perfect white sand beaches and the occasional semi-abandoned village or lone building.

"What's that?" I asked Paul, thinking that it was perhaps a simple traveller's hostel rather like the ones you get on Thai beaches.

"A drug rehabilitation unit."

This is the madness of Hong Kong. Anywhere else, it would be a boutique hotel, but here people have been too busy working to take time to appreciate the glories of nature, so it has been left to the junkies and prisoners. Even the tourists don't come here. Everybody else on the boat either lived in Hong Kong, had lived in Hong Kong, or was visiting relatives in Hong Kong.

"I've tried for years to get tourists out with us," said Paul. "But they're just not interested. I think they prefer to go shopping."

They're mad. Really, they are. We stopped at a tiny village and then got into kayaks and paddled out to a crumbling sea arch, although the sea was too rough to go through it, and then off to a deserted beach where we snorkelled above a coral reef, climbed a hill to get a view of the bay, and then paddled back to the village, where we had a slap-up lunch in a simple fish restaurant.

It's a grand day out by any reckoning. And half an hour after zooming over the waves in the Bond boat, I was back among the skyscrapers of Central making plans to meet Pete and Zuzana in a bar.

"It's the best city break in the world!" I said. All the joys of a big Asian city, and none of the stuff you feel obliged to do on most minibreaks: the sightseeing, the museums, the shopping. Instead, it's all the spirit-lifting, feel-good, hard-earned kicks you get from a walking holiday.

The next day, I head for Lamma, an island a half-hour ferry from Central, and can't believe I'm just 30 minutes away from one of the financial centres of the world economy, in a hippy enclave that is one of the last vestiges of the old trans-Asian overland trail.

There are no cars, just bicycles, and notices everywhere for "Free Healing" and "Psychic Massages" and little shops selling dodgy handmade tie-dyed things last in fashion around 1969. And everywhere, ageing western men with greying ponytails who washed up here in the Seventies and appear not to have heard that Hong Kong has become a financial powerhouse, is part of the People's Republic, and that shrooms are now illegal.

It's lovely, though, Lamma. Once you're past an ugly power station, and the hippy bead shops, it has endless footpaths and a rugged coastline. At a beach at the far end, there is just enough civilisation - spotless showers and changing rooms - and a slightly disconcerting notice: "Please note that we have taken down the shark nets for annual maintenance." I swim anyway but keep feeling things brush past my legs, make a quick exit, and head back to Central and the sharkless water of the rooftop pool of the Four Seasons hotel. I swim back and forth in the fading light, with the neon lights of the skyscrapers all around me, as transcendental an experience as you can have on any Lamma shroom.

I've gone, deliberately, in the best month - November - when the raging humidity has subsided and the skies are blue and clear. There are other Asian cities, such as Shanghai, that are even buzzier and more exciting; or more exotic ones, like Beijing; but what Hong Kong has, like Sydney and San Francisco have, is an amazing natural setting that dwarfs even its tallest buildings and its busiest highways.

With Fred, I climb Lantau Peak, Hong Kong's second-highest mountain - a relentless vertical slog, capped with amazing views. But the highlight is my day back in the Sai Kung national park with Pete, who wants to take me to his favourite beach. We do a four-hour walk that culminates at a tiny semi-abandoned village, Ham Tin, on a gorgeous deserted beach and eat delicious beef fried noodles in a beach-side shack. "Wow," I say. "You're right. This beach is amazing."

"Oh no," he says. "We're not there yet." And we climb over a final headland to the kind of beach I've only ever seen in a Seventies aftershave advert - long, rugged, backed by dunes and jagged hills, and pounded by surf. It's completely undeveloped and we had planned to camp but Pete had an early shift the next day, and since the sun was setting we figured we ought to start on the two-hour walk back to the nearest stretch of road and the bus stop. And then we see the boat. It has brought in provisions for the restaurant and the boatman agrees to take us back to Sai Kung, the nearest town, for 20 quid a head.

"What a bargain!" says Pete. "I love a boat ride."

"Me too!" I cry and we take photos of each other larking around on the beach before getting on board. When I look at them later, they remind me of photos of young men playing cricket on the playing fields of Eton shortly before being slaughtered in the Great War. We were so innocent! It takes about two and a half minutes to realise that we have made a terrible, terrible mistake. It's a flat-bottomed motor boat, the sun is setting, and as soon as we're out of the little bay, the waves are huge. Of course! That's why there was such good surf. There's a single piece of rope to hold on to and we keep on hitting the waves at strange angles and ploughing into the troughs, and the boat is very light and very flat and I'm no marine engineer but this strikes me as not ideal when it comes to not capsizing. In the dark. In the middle of the South China Sea.

"We've gone on holiday by mistake!" I say, a line from Withnail & I, although I'm not sure Pete gets the allusion, seeing as how he's clinging to the rope and making strangulated noises.

"What's the worst that can happen?" I shout over the wind with extremely faux bravado. "We'll get wet."

"It's like concrete at this speed!"

I think back longingly to my day out on the James Bond powerboat. A lovely bit of soft adventure as opposed to the half-hour, white-knuckle, terror boat ride from hell, but then the marvellous thing about near-death experiences is that when you don't actually die, the adrenaline high makes you realise why people go sky-diving or take cocaine.

We arrive back in Sai Kung in the pitch dark, our legs shaking, our hair at 90-degree angles to our heads, laughing semi-hysterically. Thirty minutes later, we step off the metro, in the gleaming Central station, still in our walking boots and with crazy hair, and bump into some friends of Pete's before joining them in a city slicker bar. They have spent the day in the office. We feel as if we've come back from the moon. It's the best city break in the world, I tell you.

Essentials

For information on hiking Hong Kong's trails, go to discoverhongkong.com. Walk Hong Kong (walkhongkong.com) organises group outings.

Carole Cadwalladr flew to Hong Kong with Air New Zealand (0800 028 4149; airnewzealand.co.uk). Returns start from £438. The Mandarin Oriental (mandarinoriental.com) has doubles from £271. Rooms at the Island Shangri-La Hotel (shangri-la.com) cost from £314.

More cities with a real wild side

Los Angeles

Just a couple of miles from LA's teeming freeways, the Santa Monica Mountains combine dramatic canyons, tranquil wilderness areas and hundreds of miles of trails for hiking, mountain biking and horse riding. Trek through the shady gorges, lined with oak and sycamore trees, in Red Rock Canyon; spot raptors and other wildlife in King Gillette Ranch; or simply leave the car on the legendary Mulholland Drive and walk into the 1,500 acres of the Marvin Braude Mulholland Gateway Park to enjoy the serenity.

lamountains.com

Nairobi

Kenya's capital city has a protected wildlife reserve on its doorstep. The Nairobi national park sprawls over 117 sq kms, with open grass plains scattered with acacia bushes, dry forest areas and some 400 different species of bird life. There are also bigger animals such as black rhino, hippo, zebra and wildebeest. The park is just 7km from the city centre, and there are picnic spots and hiking trails, although there are no accommodation options.

www.kws.org/nairobi.html

Hangzhou

The capital of China's Zhejiang province, with a population of six million people, Hangzhou is blessed by lakes, forests, tea plantations and rural hiking trails all within easy walking distance. It is home to China's only "wetland park", Xixi, which covers more than 26,000 acres, and the beautiful West Lake national park, with paths through the hills that are ideal for hiking or mountain biking, and cross-country skiing and tobaganning in winter.

visithangzhou.com

Granada

Famed for the Alhambra palace and its atmospheric gypsy quarter, Granada is also just a 20-minute drive from the dramatic peaks of the Sierra Nevada national park, the second-highest massif in western Europe. Thanks to its rare plant, bird and animal species, this is a designated biosphere reserve, with horse riding, bike and hiking trails winding their way across the peaks. In the winter, the fast road through the park means you can be skiing down the pistes in the morning, before soaking up the winter sunshine in the city centre for a late lunch.

turgranada.es