Mist still veils the pyrethrum and potato fields below, although to the south I can make out two of the other volcanoes in the Virunga chain that make up Rwanda's rugged Parc De Volcan.
After an hour of walking most of us are happy to stop climbing and stand around for a few minutes, even if it is only to examine a pile of dung.
With the prospect of another thousand-metre ascent ahead I'm relieved when the guide finally motions for silence, and begins to lead us around the flank of the mountain and down towards a large clearing in the undergrowth.
We come to a stop, and for a minute there is almost silence; just breeze coming up from the plains below and the buzzing of insects. Again, there is a sharp scent in the air, something halfway between vinegar and week-old gym socks.
It takes a minute to realise that the large ball of black wool hanging from a tree is actually a very young gorilla; it is only when it hits the ground with a thump and stands upright that it looks like an animal at all. In a flash another gorilla flies out of the undergrowth and delivers a first class rugby tackle; the two roll several metres downhill before being halted by a tree trunk.
The other gorillas come into view: two teenage males followed by first one and then another adult female. It's an idyllic scene, and we are all making the appropriate "ooh, aah" noises as quietly as we can when a huge roaring cuts us off. A branch is shoved roughly to one side, and the silverback explodes out of the undergrowth.
It's a terrifying sight, a seemingly enraged animal the size of a small bus, roaring at the top of his lungs and apparently ready to attack. He smacks his chest with one hand two or three times for theatrical effect and then, having apparently made his point, stops.
The guides mimic the belching, rumbling noises the gorillas use to express contentment, which assures them that we have come in peace, and the big male responds. The silence returns.
Charles, the silverback, weighs in at a cool 225kg, the undisputed heavyweight leader of the Umubano family of eight. Unlike human families, gorillas are always led by an ageing and grey-haired male, hence the term silverback.
Charles keeps a modest household of two wives and a handful of children, although he may choose to raid other families and enlarge his harem, gorilla society being one in which picking women up has a rather literal usage.
We've also been told to give Charles a good seven-metre breathing space, not because he is aggressive, but because being shoved off the path by a silverback can cause injuries consistent with a serious car accident.
A young male called Bunyenyeri lays back in the sun, settles his hands behind his head, and looks straight at me with what I assume is much the same intrigued expression as I am looking at him.
Gorillas live to 40 or 50 years old, and in tight family units. They spend much of their time on the ground, and although they tend to move around on all fours, they can walk upright when speed is of the essence, particularly if threatened or attacked.
It's an obvious point, but they really do look like us, just bigger, something many people find quite emotional. One woman in our group bursts into tears the moment Umurimo arrives with her two-month-old infant cradled in one arm and doesn't stop until we leave the park two hours later.
The success of gorilla tourism would not be so remarkable were it not for the violence of the country's recent past. Because for all of Rwanda's charms - and there are many - the country is still scarred by the 1994 genocide. Mass graves are everywhere as stark reminders of how the Hutu people sought to wipe the minority Tutsi community off the face of the earth.
It makes Rwanda both a discomforting place to visit and a surprisingly rewarding destination.
Mountain gorillas can be found nowhere else but this thin slice of mountainous jungle through which the borders of Rwanda, Uganda and the Congo curve.
The animals haven't always had an easy time of it: poached and sold to zoos, caught in antelope traps, hunted for souvenirs or just caught in the crossfire of myriad wars, it looked at one stage as though the gorillas could well face extinction.
There is more than one reason for their survival, but certainly the way high-spending tourists pour into Parc De Volcan has convinced most Rwandans of the value of gorilla tourism. Jobs provided by the tourism industry have provided a more stable income than poaching or trapping.
Visiting the gorillas isn't an option for many budget travellers - though it's well worth the cost of around US$850 a shot - but with only 40 places a day on offer the influx is showing no sign of slowing and places can be booked out months in advance.
After his Hollywood entrance, Charles has fallen asleep under a tree and refuses to pose. His family is less reticent. The main attractions are the kids, Ntakibazo and Izuba, whose wrestling bouts are so prolonged that in most of the photos I have of them, they seem to be a single, round and slightly blurry animal. Bunyenyeri lies back like a fashion model, chews sticks of celery, and pointedly picks his nose.
Inyongera disciplines her kids with a series of bone jarring slaps that I fear will see social services called in. And Umurimo proudly shows off her two- month-old baby in a move eerily like that once attempted by a late pop star. Eugene admits he can't be sure, but he suspects the gorillas actually like being photographed.
After an hour, we are asked to take our last pictures and head downhill, though I could have stayed all day.
Back in tiny Kinigi village there are the first signs of a tourist industry starting to spread its wings. A couple of souvenir shops have opened, selling locally made carvings and dolls, and a restaurant is due to start soon. Kids I talk to in the village tell me they are planning to become mountain guides and politely ask if I'd mind buying them a Kinyarwanda-English dictionary.
Everything about gorilla trekking has a sense of the miraculous. That the gorillas are still alive at all certainly feels like a miracle. And the fact that their continued presence is doing so much to transform an entire country is a miracle of silverback-sized proportions.
CHECKLIST
Getting there: Air New Zealand flies to Nairobi via Perth and Johannesburg with Star Alliance Partners. Kenya Airways and RwandAir connect Kigali (Rwanda) with Nairobi (Kenya) every day.
Where to stay: Prices in Rwanda are relatively low with excellent hotels such as Hotel Okapi offering lovely rooms and service for US$60. A meal in a decent restaurant costs around US$10.
Gorilla viewing: Visits to the mountain gorillas must be booked several months in advance. A small firm like Amahoro Tours is a good option.
Security: The security situation in Rwanda is calm with remarkably little violence.
Further information: See rwandatourism.com.
