Remember the opening scene in Apocalypse Now? The one where Martin Sheen's character gazes onto the war-torn streets of Saigon, cursing his torpor? "I'm still only in Saigon," Captain Willard sighs, before pressing his inner self-destruct button.m shocked to learn Francis Ford Coppola's masterpiece is almost three decades old. And it's 33 years since the Vietnam War itself trickled to a final, muddled halt.

Today, south Vietnam has changed utterly. Saigon is rechristened Ho Chi Minh City. The colonial outpost of old has mushroomed into a bustling metropolis, replete with mouth-watering food, spicy nightclubs and temperamental hotel broadband. Propaganda that once exhorted citizens to patriotism is sold as nostalgia on Le Loi Avenue. One print proclaims, stoically: "Food is the first battlefield".

My impression of Saigon (few call the city by its Communist name) is fixed from the first blizzard of hawkers and motorbikes. This is a place in flux, tangibly exciting, stuffed with the sights and smells of civilisations colliding. It is like Heraclitus' river. I could return again and again, but I know I would never visit the same city twice.

Which isn't to say it's a baby Bangkok. No, Saigon retains its French colonial boulevards, its Notre Dame Cathedral and Graham Greenesque Continental Hotel. It is dignified even as it is (unlike the older, more sedate Hanoi), unable to stand still. Vendors are everywhere. Neon signs hang above Notre Dame's Virgin Mary. Air-conditioned malls and five-star hotels spring up willy-nilly, just as there are boxes of puppies for sale outside Reunification Palace.

Early on, I visit the roof-top bar at the Rex Hotel, from where the Americans delivered their 'five o'clock follies' to journalists during the war. It is a feast of tack -- a green-lit balcony, buffet dinner and extortionately priced beer accompanying the view over a honking intersection. It's also where Christina Noble first pitched up in Vietnam, gathering street children into her room for baths, clothes and food.

It strikes me pretty early, too, just how friendly the Vietnamese can be. This is a notoriously self-conscious, one-party state, but stand still for no more than a moment, and someone is over to inform me that English has 12 tenses. And what, he inquires, is the difference between 'affect' and 'effect'?

Later, over a snap-fresh dinner at Ngon restaurant, I am poking through a fire-hot chilli sauce when a waitress pre-empts my query: "Chilli, potato, onion and a little oil. Just a little oil," she says, before disappearing like a friendly ghost. Total bill: less than €7.

The motorbikes, of course, are another matter. "It's like fish traffic", says one guide, observing the shoals swarming around us at traffic lights. They hum and rev, beep and honk, morphing like amoeba around anyone trying to cross the road. And, of course, they carry literally anything -- mattresses, fruit, people. More than two million of the things exist in Saigon alone, a fact which makes for some hairy road-crossing.

The War thing is strange. Say the word Vietnam and Westerners conjure up images of jungle battles, America in the mother of all quagmires, and movies ranging from The Deer Hunter to Platoon. The government here is fed up explaining to us that Vietnam is a country, not a conflict. "It's a fact," Vu Tuan Dung, a government press officer, says. "It's sad."

Interestingly, however, there appears to be little residual bitterness. Most of Vietnam's 85 million souls are less than 25 years old, with no direct memory of what they term the 'American War'. And besides, many in the south believe the Americans were trying to help. Whatever about the north's ultimate victory, as Mr Dung points out, people don't tend to kick up about political systems once they offer the potential for prosperity.

Despite all of this, the war remains a draw. T-shirts and souvenirs are for sale on every street corner. The American embassy is a photo op. Rambunctious bars like Apocalypse Now and Heart of Darkness (no, really) pander to western revellers. Thankfully, though, the city carries its share of edifying memorials too.

The War Remnants Museum is one such oasis, arranged around a courtyard of tanks, guns and bombs. Eight exhibition areas treat the war and its aftermath, and the photo-heavy display manages to be both iconic and shocking (note to the faint-hearted: avoid the foetuses-in-jars section). Alarm bells go off when you see a title like 'Historic Truths', but all told, the effect is thought-provoking. It doesn't require propaganda, after all, to demonstrate that Vietnamese lives were worth less than their western counterparts. In many ways, they still are.

The other major Vietnam War attraction is, of course, the legendary Cu Chi tunnels. Around 40km north-west of Saigon (the drive offers a wonderful passing glimpse at rural life), the subterranean complex connects some 200km of Viet Cong tunnels dug as a furtive commune and, later, a major base for the Tet Offensive. It is a fascinating visit.

Cu Chi is today laid out as a forest trail, and its touristic rebirth aims to give an insight into the life of a Viet Cong guerrilla. Stops include a US tank destroyed by landmine in 1970, B52 bomb craters, a ghastly array of mantraps and, bizarrely, a shooting range where one can fire an AK47 at $1 a bullet. Shooting the thing appeals to my inner Homer Simpson (and is surprisingly tough physically), but I can't help thinking tourists and live ammunition shouldn't really appear in the same sentence, not to mention a firing range.

The tunnels themselves arrive out of the blue. We stop walking, our guide brushes away some foliage and uncovers a trapdoor the size of a tabloid newspaper. He lowers himself in, disappears, and invites us to do the same. I am five foot 10in, and of average girth, yet I can't even squeeze my shoulders through.

"They made the original a little bit bigger," he says, leading our group to a specially adapted section where tourists can wriggle along for 20 metres or so. "If they didn't, there is no way you guys could get through."

Far less constrictive a proposition, and deserving of more than a day trip, is the deeply verdant Mekong Delta. Bottling its way from Tibetan Plateau to South China Sea, the Mekong spills some 475 billion cubic metres of water every year, making this region Vietnam's rice bowl. It is an awesome force of nature, described by Captain Willard as snaking through the war "like a main circuit cable plugged straight into Kurtz".

Here, you have at once the real Vietnam and the postcard image. At Can Tho, a staging post for river trips, floating markets kick into life at 6am. Tiny boats sell to small boats, small boats to big boats, and big boats to bigger boats in a watery exchange showcasing everything from limes to pumpkins and yams. Vendors advertise their wares on bamboo poles rammed into the prow.

The best thing about the Delta is watching life pass by. Sure, there is a lot of waiting on ferries. But to witness Buddhist altars in back yards, children waving from riverbanks, water hyacinth floating seawards, or farmers in conical hats (non la) tending rice amidst water buffalo and coconut trees, is to witness a window into another world. Vietnam is a country in flux, everyone will tell you that. Here is what it is in flux from.

Back in Saigon, I get a dose of the monsoon. Colourful ponchos dash about, rain thunders down, lightening flashes electric blue. On this visit, I hit the markets -- Bin Tayh and Ben Thanh -- with their stores stacked together like shoeboxes. "I recommend you a trick," says Le Quang Nhat, a local photographer. "Please deal with them one third the price!"

Nhat meets my companion and I at Highlands Coffee, offering his tuppence on this scintillating comet of a city. The suburbs are buckling he says. Migration is crazy, development unchecked. The Saigon River is putrid, the motorbikes incessant. Change and the colonial core are locked in continual tension. But, contrary to Willard, he loves it.

"It's a real smiling place."

- Pol O Conghaile