In the lesser trod reaches of Asia, border crossings can be a tedious and time-consuming hassle. Visas, queues, admin, logistics and the often unwelcome attention of jumped-up border guards with little to do but intimidate hapless travellers who put the wrong tick in the wrong box. Sure, you can jump on a plane and take the easy airborne route through air-conditioned airports, but where’s the fun in that?

I’d just spent a most agreeable week cruising overland through Cambodia. From the archaeological wonders of Angkor Wat where I saw the solar eclipse turn an already surreal landscape into something otherworldly to the southern fringes of Sihanoukville, where the infamous hippy party town was celebrating its final death throes before the Chinese developers moved in and ‘legitimised’ the decades-old shacks and shanties with concrete monoliths and soulless skyscrapers.

Onwards south I’d boated out to the private islands of Song Saa, where luxury comes with a conscience and my £1,000-a-night villa was helping fund the development of local communities, protecting marine environments and shining a new light on the power of sustainable luxury tourism.

But now, heading back to the capital of Phnom Penh my eye was firmly fixed on Vietnam and the next leg of my trip. Some research had given me a few options for crossing the border – a flight into one of several metropolises (which I’d already ruled out), the five-hour Victoria speedboat ride to Chau Doc on the Vietnam border (fun but way too rushed), or a leisurely three-night cruise along the Mekong Delta dropping me off in the centre of Ho Chi Minh City (officially renamed from Saigon on 2 July 1976). No contest, then.

Heritage Line’s Jayavarman comes straight out of the Agatha Christie school of river cruising. Finished in royal blue with elaborate metalwork and teak cladding, I boarded half expecting to be met by a bumptious Peter Ustinov, all twitching moustache, knowing chuckles and presumptions of whodunit.

From my beautiful spacious cabin to the classically finished dining room complete with big brass bell (sounded to signal mealtimes) and the open-air pool on the top deck, it promised a sumptuous, sedate way to travel. I wasted no time familiarising myself with the amenities as we chugged serenely out of Phnom Penh and on towards Tan Chau where we would cross into Vietnam.

Hours later and Sentot, the Jayavarman’s manager appeared, politely requesting my passport as we slowed to a stop amid a queue of commercial ships and local river traffic plying their trades. Rousing myself from the pool, Sentot indicated I should stay put as he sped off to take care of border business. Thirty minutes later we were Ho Chi Minh bound once more – and I hadn’t even reached for my towel. It’s as civilised a border experience as I’ve ever had (or likely will have).

Boys and men of all ages chug on ciggies before diving into the murky waters amid tangles of nets and tubing,

After a night moored midstream on the fringes of Vietnam’s great waterway, we head out early to explore bustling Tan Chau, ferried on xe loi – two-person bikes with fixed trailers pedalled by smiling locals who weave among traffic with nerve tingling dexterity. A short hop on a local ferry brings us to one of the Mekong’s most extraordinary sites – the floating catfish farm villages where residents breed their livelihood literally under their feet.

We watch up close as boys and men of all ages chug on ciggies before diving into the murky waters amid tangles of nets and tubing, common garden hoses clamped between their teeth delivering life-sustaining oxygen from a wheezing generator as they wrestle nets weighed down with hundreds of pounds of struggling catfish to the surface. It’s a pretty terrifying sight, with the divers often gone for ten minutes or more before finally resurfacing with toothless grins to shouts of triumph from us amazed onlookers.

Later that day, as we wend our way further into the Mekong’s grip, we stop off at My An Hung village. Here, a local family puts on a dancing display with giant dragon puppets and the village elder throws out some traditional Vietnamese tunes on his electric guitar, his besotted wife eyeing him up lovingly as he rocks out. In the background local kids hurl themselves off a rickety ‘monkey bridge’ into the reed-strewn waters and the sun sets in a rainbow of oranges and violets. This Mekong life is magic, I think to myself.

Day three dawns and we head out on our final excursion: a traditional wooden Sampan boat takes us into the mayhem of Cai Be’s floating market where local traders hawk fruits, vegetables, and all things rice: paste to paper, cookies to wine. Colourful, noisy, a sensory assault – it’s the Vietnam as laid out in the pages of brochures and catalogues brought to life in sensory overload.

Slowly, surely the now familiar Mekong landscapes start to change. Urbanisation creeps in, wooden sampans are replaced by hulking metal motorboats, muddy riverbanks give way to grimy ports and jetties, and the ever-present river aroma is overwhelmed by the taint of diesel and sewerage. We slowly draw into My Tho for a short bus ride into the centre of Ho Chi Minh City.

A different world – to me something like Bangkok crossed with Los Angeles – Ho Chi Minh City is a metropolis bursting with modernity and weighed heavy with history.

I have only one day here before my final stop, and so I take the tourist route. A sombre but eye-opening stroll around the War Remnants Museum; a visit to the extraordinary Thich Quang Duc memorial park commemorating the venerable monk who self immolated in protest at the government’s treatment of Buddhists (immortalised in pop culture on the cover of Rage Against The Machine’s eponymous album); and lastly to Independence Palace whose gates were famously breached by a North Vietnamese tank – the photo of which came to represent the fall of Saigon.

It is now known as Reunification Palace.

That name change typifies my experiences scratching the surface of Vietnam, this country of contradictions. Where the Mekong’s time-frozen subsistence-led lifestyles, reflective of the communist mentality, rub shoulders affably with a high-rise city so capitalist in its appearance they could be from the opposite ends of the earth. A startling introduction to an extraordinary place, if only every border crossing could be so seductive.

In Cambodia, Duncan stayed at the Raffles hotels (raffles.com) and Song Saa Private Island (songsaa.com). He cruised across the border on the Mekong aboard the Jayavarman with Heritage Line, bookable through Cox & Kings (coxandkings.co.uk).