Crossing the road is the first big challenge here. There are approximately 8 million people in Vietnam's biggest city, but it seems like there are twice as many motorbikes. Once you've mastered the art of calmly walking out into six lanes of traffic, this fascinating city opens up to you. Although it's true that HCMC is more westernised and cosmopolitan than Hanoi, this is still very much a Vietnamese city, a place where tourism feels incidental.

I spent my days savouring the fresh and zingy flavours of Vietnamese cuisine - a hearty pho soup for breakfast, a banh mi baguette for lunch stuffed full of barbecued pork, a bowl of bun cha noodles for dinner - while wandering the streets observing the everyday sights that bring Vietnam to life. Builders crowding round streetfood vendors, workers in conical hats tending the city's parks, and selfie stick-wielding tourists from the provinces snapping pictures in front of Ho Chi Minh's statue or the soaring spires of Notre Dame cathedral.

Ho Chi Minh City is Vietnam's commercial capital, and the shimmering skyscrapers are multiplying by the day. But recent history still looms large here, as I discovered at the sobering War Remnants Museum. Although the exhibits are inevitably partisan, some of the most shocking photos on display were taken by American journalists during the Vietnam War, documenting the notorious My Lai massacre. Equally upsetting is the exhibition dedicated to the lingering effects of Agent Orange, the chemical defoliant which left a terrible legacy of birth defects and poisoned land.

Although Ho Chi Minh is a busy city, there are quieter spots where you can take some time out from the hustle and bustle, such as the incense-shrouded Jade Emperor Pagoda, or the eerie Independence Palace, the former headquarters of the South Vietnamese government which has been left more or less as it was when Saigon fell in 1975.

After four days of big city buzz it was time to experience a very different Vietnam, as I headed south to the port of My Tho on the Mekong delta, just under two hours' drive from Ho Chi Minh City. Here I boarded the Tonle Pandaw, a beautiful colonial-style vessel with just 28 cabins. As I settled in I got my first glimpses of life on the river; overloaded barges chugging along laden with sand, rice and timber; little fishing boats casting their nets close to the river banks; and everywhere clumps of water hyacinth floating on the surface, in places creating a carpet of green that tangles up propellers and strangles other plants.

Pandaw's intimate and laid back vessels are a perfect fit with the languid rhythms of the Delta. My cabin was compact but comfortable, with all the essentials like air-conditioning and ample storage, plus a surprisingly spacious bathroom. Although the cabins don't have balconies, they all open onto a wraparound communal veranda with seating outside each cabin. Much of my time on board was spent up on the sundeck, most of which is shaded and cooled by fans. Comfy seats and sun loungers allow you to relax while watching life on the river go by, with a bartender on hand to mix you up a gin and tonic or a cocktail as the sun sets over the Delta.

The ship also has an indoor saloon bar, which comes in handy if it rains, plus a small spa, boutique and cinema room. The dining room enjoys plenty of natural light during the day, and the excellent food draws heavily on the cuisine of Vietnam and Cambodia. Each day the buffet lunch was supplemented by something special like a noodle station or a whole suckling pig, while dinner was either served à la carte or 'family style', where a selection of dishes is brought to your table and you help yourself. The wonderful crew were all from Vietnam or Cambodia, with the exception of the purser, Jimmy, who was Burmese.

My cruise along the Mekong was a far more immersive experience than any ocean cruise I've been on, and I really felt like I saw an authentic slice of Vietnam and Cambodia. Each day we went out on excursions in small groups, with QuietVox headsets provided so you can always hear what the guides are saying. It's worth pointing out that this cruise is not really suitable for those with walking difficulties; most days we were coming ashore at small jetties, sandbanks or rickety bamboo walkways, with little in the way of infrastructure.

On our first morning we visited the town of Cai Be, where we cruised amongst boat-based vendors selling their wares at the floating market, and we were taken on a tour of local producers who showed us how they made rice paper, coconut candy and whisky. After a walk through the town we were transferred to small two-person rowing boats for a short journey through narrow backwaters, where the vegetation closed in around us and the cicadas buzzed ever louder.

In Sa Dec we visited a chaotic market, where motorbike traffic weaved in and out of the locals and boggle-eyed tourists perusing the stalls piled with fresh fruit and veg, flowers, live eels, catfish, frogs, chickens, rat meat, 'hundred year old eggs' and much, much more. The rush of sights, smells and sounds are really what Vietnam is all about, and we stumbled out the other side still trying to process everything we'd seen.

Other interesting excursions included a visit to a Cham village in Chau Doc; the Cham are an ethnic group that inhabited this part of Indochina before the Vietnamese moved in, and there are communities dispersed across Vietnam and Cambodia. In this part of the Delta the Cham people are Muslim, with a different culture and their own language, dress and handicrafts.

I'm often surprised by how abruptly things can change at national borders, and the crossing into Cambodia was a case in point. After the bustling Mekong of Vietnam, where the river traffic was constant and the banks were lined with fish farms, market towns and factories, the Cambodian stretch of the river seemed almost deserted. The scenery instantly became more rural, we barely saw another boat on the river, and the intricate outlines of Buddhist temples began appearing along the banks.

Finally we arrived in Phnom Penh, where my journey on the Lower Mekong came to an end. The Cambodian capital had visibly changed since my last visit six years earlier, with more towers and more bright lights fuelled by Chinese investment, but this plucky city retains a unique charm. Before disembarking we took a short cyclo tour, visiting the impressive Royal Palace and browsing the bustling Central Market. Cambodia is a country with a difficult recent past, on display at the harrowing Genocide Museum and the notorious Killing Fields, but the optimist in me says that it's also a country with a bright future.

A river cruise is a fantastic way to experience Vietnam and Cambodia, whether it's a short itinerary like mine that can slot into a land-based tour, or an extended voyage that carries on to Siem Reap and the temples of Angkor. Pandaw offer more options than anyone else on the Mekong: they're the only company with ships that can reach Kratie, home to the rare Irrawaddy river dolphin, and they also offer unique itineraries on the Upper Mekong in Laos and China. If you're looking for an immersive, destination-focused cruise on an intimate and characterful ship with superb onboard delivery, Pandaw is the perfect choice.