Our temple pilgrimage begins with impeccable chronological logic at 7th-century Sambor Prei Kuk, a prototype Khmer capital from 200 years before Angkor. It is so far gone in forest that I don’t see it coming. A monstrous octopus is eating the gatehouse — Tra says it’s a strangler-fig tree — and beyond, crumbling brick shrines scatter like stamped-on sandcastles through the jungle. The only other visitors are two backpackers, and the tourist infrastructure amounts to three ragged boys with scarves draped over their forearms, who trail behind us from temple to temple like pages — steadfast and silent, never once begging a sale.

We wander between the sanctuaries, dipping into their cool, kiln-like interiors, inhaling the solitude. The sun-spangled woods feel curiously English, more Christopher Robin than Mowgli — though, as far as I know, Christopher Robin never grappled with huge female pudenda. These are the yoni — suggestively shaped altars secreted inside each shrine, and originally pierced by the sacred phallus of the Hindu deity Shiva.

The stone members have long since been plundered, but inside one sanctuary we find evidence of continuing worship: a shapeless boulder draped in a scraggy orange krama, the Cambodian scarf. Tra thinks it’s a totem set up by villagers to the spirits of health or harvest — their flyblown offering of rice and incense speaks of the animist beliefs of the Cambodian countryside. Asia’s earliest temple city may be tumbledown but it seems nobody remembered to tell the locals it was “lost”.

We jolt on northward on bomb-site roads, the scarlet skulls multiplying, the jungle pressing in. To the west lies tomorrow’s target, Koh Ker, where I’ll scramble to the top of a 120ft pyramid on a rickety ladder and find myself sole overlord of a 10th-century settlement almost as big as Angkor — a hundred of its monuments still lurking, unclaimed by archeology, somewhere in the undergrowth.

But tonight we plan to camp at the furthest-flung wonder of the lot: Prasat Preah Vihear, the “Great Temple in the Sky” — three centuries’ worth of super-intricate gods and monsters chiselled straight into a cloud-snagged mountaintop by successive Angkor emperors. The journey time is unpredictable: it depends how many plank bridges are down and how many stops you make to drag crumped Land Cruisers out of a ditch. On our trip it turns out to be one of each — plus one mini-monsoon that soaks us through as we batten down the roof rack. Six hours in all, by which time our driver, Siha — button- collared and bespectacled when he picked me up at the airport — is bare-torsoed and bulging-eyed, with his krama knotted round his forehead like Ben Gunn.

The last half-hour is straight up the side of the Dangrek mountains on hair-whitening hairpins, the road crumbling under our wheels like in a Hitchcock car chase. A hilarious three-inch kerb separates us from gory oblivion.

It’s worth it. At the top, mist froths mythically around a mighty pink causeway, pedlars wobble under the weight of milkmaid-type yokes, and a few Thai day-trippers from the other side of the mountain straggle back to their cars. Yes, there are other people around — but that’s where our tents come in. It is four o’clock, two hours till dusk: time to spend completely alone with the Angkorian ancients.

While Siha and the rest of our retinue make camp, Tra and I set off to climb the staircase of broken-topped sanctuaries towards the temple summit, swarming hand-over-hand across a terrifying rubble of Hindu iconography: writhing serpents, gaping birdmen, mad-eyed demons. This is Indiana Jones made real: along shadowy corridors, into flooded vaults, never sure whether you’ll find Buddhas or bats. We finally emerge onto a craggy balcony 2,000ft above the jungle, where kings once came to greet their gods. Sunset seeps across the plain; the roar of the cicadas is lion-loud. It’s quite incredible.

As we descend again, Tra points out pockmarks in the temple ramparts: “Gunfire. The Khmer Rouge retreated here in the 1990s. Preah Vihear was their last stand.” When we get back to camp, now perfumed by tree-resin torches, Chung the cook is dishing up chicken with lemongrass. It’s the most astounding camp site I’ve been to, knocking Happy Valley Caravan Park and Silage Plant, Porthmadog, into a cocked hat. I feel privileged to be here, and very well looked after. Time to crack open my sunnies case and hand round the spider legs.

Travel details: Audley Travel (01869 276360, www.audleytravel.com) has nine nights in Cambodia from £1,895pp, including flights from London, a two-night temple safari, four nights in Siem Reap and two in Phnom Penh. Or try Regent (0870 499 0911, www.regent-holidays.co.uk.

The safari can be booked independently through Hanuman (00 855 23 218356, www.hanumantourism.com): the two-night tour, starting from Siem Reap, with a guide and meals, costs from £350pp.

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