The Chyulu Hills form the northernmost part of Tsavo West, an ecosystem characterised by savannah woodlands, solidified lava flows and volcanic hills straddling Makueni and Taita Taveta Counties.

Chyulus are the “Green Hills of Africa,” a paradise that inspired Ernest Hemingway’s book of the same name — when it rains, the sunburned hillsides are transformed into a verdant green like a golf course.

From Nairobi we drove down Mombasa Road and turned southwest after Emali town onto Loitokitok Road, which leads to the Amboseli and Tsavo parks. Mt Kilimanjaro came into view, and would be our constant companion over the next few days.

At the Mbirikani intersection, we branched left onto a murram road leading to the Chyulus through group ranches managed by local Maasai. Chyulu is one of the youngest volcanoes, and the last eruption was in 1855. There are lava tubes — cylindrical passages hollowed out by hot molten lava — inside the hills, locally known as the Kisula Caves. The tubes lie at different depths and the Upper Leviathan Cave, measuring 11.5km, is said to be one of the longest in world.

You can hike from the foothills to the caves, a trek of about three to four hours, but we chose to drive there instead. Then, armed with flashlights, we descended into one of the tube-like caverns.

Kisula Caves resemble a natural art gallery, with walls of different coloured rocks, rippling layers of sediment, cone-shaped stalactites hanging above and sections of rock wall where the lava has cooled off into rope-like shapes.

In some sections, the cave was completely dark and at other places sunlight flooded in through the sinkholes overhead. There were bones on the sandy floor, leftovers from leopards’ meals. Bats and baboons also inhabit the caves.

There are two lodges on the Chyulus, both luxury accommodation and definitely worth the pampering. For the more frugal traveller, there are campsites; hiring a ranger from the Kenya Wildlife Service (KWS) is advisable. More often, visitors drive in from lodges in Tsavo West National Park, which was our next destination.

The Chyulu Hills rise to 2,188 metres, and the upper sections are covered by a thick forest where morning dew and moisture-laden clouds water the lush foliage.

Unfortunately, we were informed that the roads further up were not in good condition, so we could not explore the forest. Rain water in the Chyulus percolates into underground reservoirs and undergoes natural filtration for years before permeating through subterranean channels. The water merges with networks from Mt Kilimanjaro and feeds into watercourses such as Mzima Springs, some 50km away.

Mzima Springs is a luxuriant green oasis in the middle of the Tsavo West bushland. The crystal clear water gushes out of lava rocks and into large pools fringed by reeds and raffia palms.

Vervet monkeys prance on the sycamore figs and yellow-bark acacias as we walk along the pedestrian path. Hippos and crocodiles live in the Mzima Springs, hence the presence of armed KWS personnel to escort visitors.

The hippos emerge from the water at night to feed in the surrounding grasslands, returning at dawn to loll in the water all day. They sleep underwater, mate and birth underwater, and are astonishingly fast swimmers. We watched them poke their noses above to breathe for a few seconds before submerging.

The dung from the hippos feeds insects and fish, which in turn feed the birds. The Springs are rich with the sound of birdlife, and I saw a kingfisher perched on a bough keenly scanning the water below. If you go down into the underwater viewing room, you can watch the fish swimming.

The river arising from Mzima Springs flows for a couple of kilometres before vanishing underground, headed for the coast. Producing over 200 million litres daily, the Springs supply water for the Mombasa, Kwale, Kilifi and Taita Taveta Counties.

The following day we headed west to the Shetani lava flows. Located about 5km before the Chyulu Gate of Tsavo West, Shetani (meaning devil in Kiswahili) is a flat treeless plain covered in dark rocks and sharp stones left behind by lava flows hundreds of years ago.

The bleak landscape of Shetani looked strangely beautiful under a clear blue sky and a palpable silence except for a strong wind blowing.

Not far away are the Shetani caves, which can be explored. Only a few bushes and klipspringer antelope survive in this black plateau.

Our driver-guide informed us that the ground at Shetani still moves because of continuing seismic activity, a disconcerting thought while standing on the path of a lava flow.

Apparently, he says, if you set a stone in a particular place and return a week later, the stone will have shifted.

This phenomenon, together with the living-memory volcanic eruptions, very likely added to the local mythology that gave rise to the name of the place.