No matter the opinion, hundreds of thousands of tourists head to the site to at least get some idea of what it was like for fighting sides during the Vietnam War. It’s here visitors can explore the intricate underground network of tunnels – a 75-mile underground maze where villagers and those loyal to the communist movement fought, ate and slept at the height of the fighting. Crude weaponry used during the underground campaign is displayed in a grisly exhibition of how soldiers met their untimely deaths. It came unexpectedly for most, with many falling into poisoned stake pits. But the final minutes of life must have been excruciatingly painful.

These days, the only obstacles tourists face are the lines of tacky souvenir vendors. Westerners who experience the claustrophobic conditions underground and sample the crap food once consumed there can now buy a bullet on a chain as a fitting memento.

But many would argue the legacy the Vietnamese would rather leave visitors with is found in the busy streets of Ho Chi Minh. At the War Remnants Museum, patrons are shown a catalogue of recorded horrors from the duration of the campaign, with gut-wrenching images of destruction, torn corpses and documentation of US force’s alleged war crimes. It’s not for the faint-hearted.

An American tank and helicopter displayed outside the museum serve as fitting reminders of the US force’s artillery strength. But in another corner, two large glass jars hold the preserved remains of stillborn Siamese twins and a second deformed baby – a result of Agent Orange chemical spray contamination – and a clear reminder that the affects of the war continued here long after it was over.

To tour this exhibition is to see a side of the conflict few have probably seen. Some are quick to label it propaganda; others, though, probably leave with a greater understanding of the capacity of the human spirit and the sort of things people will do to one another when completely drained of it.

But it’s across Vietnam’s southern border, over the rich and diverse waters of the Mekong Delta and into the rice fields of Cambodia, where tourists face something far more confronting.

Less than an hour from the capital Phnom Penh, up a dusty unsealed road, past shabby village huts and stalls on a property once used by farmers, hundreds of human skulls lie stacked on top of each other in a shrine of remembrance at the Cambodian Killing Fields.

Huge mass graves mark the resting place of thousands of men, women and children murdered during the rule of the communist guerrilla group the Khmer Rouge. After taking power in 1975, the movement led by Pol Pot, tortured and killed on an unimaginable scale. An estimated two million Cambodians died. Everybody was put to work in fields outside the city and those who refused were killed: educated professionals, ethnic minorities, it did not matter. There was no escaping the brutality.

The majority of visitors probably arrive with the sole purpose of ticking another box on their travel agenda. But it would be hard to walk away not having been affected by what they see here. Below the shelves of human skulls lie hundreds of clothing articles recovered from the bodies of those buried in the surrounding grounds. Elsewhere, human bones lie stacked or scattered around sunken pits where people of every age were abused, beaten, tortured and executed.

But it’s at S-21 – an interrogation centre in an old suburban high school back in Phnom Penh – where tourists are really forced to contemplate how evil this regime became.Thousands of black-and-white pictures of nameless Cambodian prisoners line the walls of each room, every one of them the last recorded image before they were tortured and killed. On some walls, uncertain faces are tacked beside images of battered corpses in macabre before-and-after shots.

It is very hard for your average budget traveller to comprehend and, for a moment, reason enough to feel guilty for enjoying a holiday experience here. Sure, the beer may be cheap but it doesn’t sit well when you contemplate how so many died across these two countries for no real reason.

It is nevertheless what a traveller to this part of the world need prepare for. There are, of course, plenty of other reasons to visit. Both countries boast long sandy beaches, wild jungle experiences, temples and cities bustling with everything you’d expect from this region. To visit Vietnam and Cambodia is to delve into the past driven by dispute, war and tragedy. But it’s as much about appreciating the tenacity of people who have come through it all and still have a smile on their face.