Local tour operator East African Eco Adventures was keeping us fed and sheltered, shuttling our tents and provisions from one campsite to the next and creating disarmingly good evening meals from regional ingredients. I’d previously had no inkling that charcoal-roasted goat could be so tender, nor that river-caught catfish was quite so moreish. Such were the joys of walking up an appetite. Our campsites varied greatly – on one night we slept under the stars, bedding down on top of an old Land Rover – and the landscapes were just as diverse. On the scorching valley floor we walked among thorny scrub and flat-topped acacia, while in the highlands we wandered through cool pine groves, treading a path between tomato and coffee plantations.

Flowers shone from the undergrowth. Huge views tumbled out and down, full of green slopes, farming terraces and rippling rock formations. It struck me that some things would have changed little since explorers such as Hannington and Thomson were here more than 130 years ago. The walk held magical moments. On the evening that we reached the village of Maji Moto, a luxury was revealed in the form of a natural thermal rock pool. We tore off walking clothes and sank into the deep, warm waters just as fireflies were emerging from the trees. In the Great Rift Valley, the days of hiking are long, sometimes shatteringly so, but they’re more than worthwhile.

Royal approval – Somewhere in the folds of the Tugen Hills, the belt of peaks that runs down the middle of the valley, there lives a young boy named Tonyblair Jepkurui. His mother Ester had joined us for our penultimate day’s hiking. “No, we don’t admire the man,” she told me patiently, resplendent in an emerald-green Kenya football shirt. “We just admire the name, from the news. We wanted a name that was different.” The former PM isn’t the only Brit to have made an impression of sorts here. In 1955, the Queen – then Princess Elizabeth – famously had to cut short her holiday to Kenya when her father died. One of the spots she was due to visit was a campsite high in the hills, now known as the Royal Camp. When we arrived there mid-afternoon, a group of 80 local girls on a school trip were stood singing gospel songs.

Their voices spilled up into the sky. At first light the next morning, meanwhile, Mount Kenya, Africa’s second-highest mountain, stood noble on an orange horizon. A site fit for royalty? No question. The week continued to produce surprises. I knew that the Big Five didn’t frequent this part of the Rift Valley, so hadn’t expected much wildlife. I was wrong. “Look, zebra,” I said Jackson one morning – I followed his finger and saw four nearby in the bush. More animals were to follow. We saw tortoises, mongooses and monkeys. Pairs of dainty dik-diks sprang up rocks. Baboons lumbered across the trail. Gentle impala drifted away from us. The birdlife was remarkable too: yellow-billed hornbills, lilac-breasted rollers, green wood hoopoes and my personal favourite, the white-bellied go-away bird.

At times, the heat was an issue. Midday in the tropics is not always a great friend to hikers. But it’s worth noting that walkers aren’t obliged to cover the entire distance -half-day treks and 4WD pick-ups are easily arranged if desired. Indeed, when Jackson and I reached the main tarmac road that stretches up the Rift Valley from Nairobi to South Sudan, we opted for a vehicle transfer rather than an hour of roadside hiking. “The trail can be as hard as people want it to be,’’ William had told me. “Crossing the valley is the important thing.” When we clambered and clawed our way up the valley’s 3,000m-high western escarpment to finish the trek, I felt the sense of achievement that comes from completing a long, hard yomp.

As much as the landscapes had been magnificent, however, the people I met along the way will linger in the memory for just as long: the softly spoken man who had turned production of the local honey, garnered from basic log hives, into a community cooperative; the beaming woman who rushed chai tea and chapatti flatbreads out to us in the lunchtime shade; the 70-year-old who had been walking this same trail all his life, and had four wives and 25 kids to show for it. Hotel beds and hot showers awaited us on the final night. Breakfast the following morning was on the balcony, looking back across the cloud-patched valley, back across the cradle of mankind. “The Kalenjin language has no word for goodbye,” Jackson had told me earlier in the week. “Only thank you”. It seemed apt, somehow.