We dropped down on our knees and gingerly peered over. Sheer walls plunged down into a swirling white void of mist and vapours. We could hear a roar like the sea from somewhere far below. We could feel warm air rising. We could smell sulphur, and see columns of steam escaping from fissures in the walls. But of the world’s biggest lava lake in the crater’s base we could see absolutely nothing. We were the first travellers to tackle Nyiragongo for at least two years, and we were bitterly disappointed. But what we did not know at that moment was that within a few hours we would be spectacularly rewarded for our efforts.

Only for the brave – Nyiragongo stands in Virunga, Africa’s oldest national park and a UNESCO World Heritage site, whose 7,700 sq km encompasses snow-capped mountains, glaciers, forests, savannahs and eight volcanoes – two of them active. The park also boasts more animal species than almost anywhere else on earth, which means that – within 24 hours of climbing Nyiragongo you can be standing in | a tropical forest, staring into the uncannily human eyes of a huge | mountain gorilla. Of the 900-or-so of those critically endangered l animals left in the world, Virunga boasts roughly a third.

For most of the past two decades Virunga has not just been closed, it’s been the epicentre of the seemingly endless conflicts that have cost five million Congolese lives and made the DRC a synonym for warfare and brutality. It has been infested by armed rebel groups that have poached its wildlife and plundered its forests. Much of it still is – and the Foreign & Commonwealth Office still advises against all travel to eastern Congo. However, since November 2013 a fragile peace has prevailed, and earlier in 2014 the park authorities re-opened its southern section.

It remains edgy, and no place for the physically frail or those of nervous disposition. But for the more robust traveller it offers the unforgettable experiences of Nyiragongo and the mountain gorillas, an almost total dearth of other tourists, and the breathtaking scenery of a raw, untamed part of Africa. Nor do you need to forsake comfort, for the park has also re-opened Mikeno Lodge, a relatively luxurious retreat in its Rumangabo headquarters complex, which was built during a lull in 2011 but mothballed when the fighting erupted anew six months later. The park’s staff took refuge in its wine cellar as artillery fire echoed all around.

Quite a ride – To reach Virunga I flew overnight from London to Nairobi where I met Mikey Carr-Hartley, a professional guide who plans to take small groups to Virunga and wanted to scout it out. Together we took a connecting flight to Kigali, capital of Rwanda, and then a three-hour taxi ride to the Congolese border town of Coma. We passed the mountains where Dian Fossey, author of Gorillas in the Mist, worked with the greatest of the great apes for 18 years until she was murdered there in 1985. You can see mountain gorillas in Rwanda, too, but you’ll be part of a larger, regimented party and the animals are much less wild. Crossing the border was a shock. In a hundred metres we went from the first world to the third.

We were met by a Virunga Land Rover and the armed rangers who, for the duration of our visit, accompanied us everywhere we went. We drove through Coma, which is full of UN troops and NGOs, and northwards up a ribbon of rutted mud and rock and lava that was once a fine paved road. Volcanic peaks with forested flanks and shrouded summits rose to the left and right of us. People tilled fertile fields of beans, maize and potatoes. The sides of the road were lined with rudimentary wooden shacks. The road itself was a river of humanity – colourfully dressed women carrying impossible loads on their heads, ragged children playing soccer with balls made from rolled-up plastic bags.

Men pushed extraordinary wooden contraptions called chukudus; these beasts of burden, unique to this part of eastern Congo, resemble giant children’s scooters or something out of a Flintstones cartoon. Their long running boards are attached at the front to tall upright shafts topped with handlebars like bulls’ horns. Their wheels are made from thin slices of tree trunk with strips of old tyre wrapped round their edges. They are used to transport huge bundles of timber or bamboo, great bags of cement or charcoal, scarcely credible loads of fruit or vegetables. Cheap and sturdy, chukudus are masterpieces of improvisation built to cope with conditions unlike those anywhere else in the world.

We saw army emplacements too, and a piece of heavy artillery abandoned by some militia, and the spot where Emmanuel de Merode, Virunga’s director, was ambushed and seriously injured by unknown gunmen in April. The British-educated Belgian has made many enemies since he was brought in to regenerate the park in 2008: the armed groups that still inhabit its northern and central sectors; the poachers who have killed thousands of its elephants and hippopotami; those who cut down its forests for charcoal; even a British company called Soco whose search for oil in Virunga he has fiercely opposed.

We eventually turned on to a dirt track that wound high up into the mountains and was almost impassable, even in a 4WD. For another excruciating hour we clung to the vehicle’s straps as it lurched from side to side, chased by barefooted children dressed in Oxfam cast-offs, past mud-and-bamboo huts with banana-leaf roofs. Finally, mercifully, we reached Virunga’s new Bukima tented camp. It was worth the journey.

Bukima was hardly glamping, but the tents were clean, dry and comfortable, and enjoyed spectacular views across a green valley to no less than three mist-swathed volcanoes – Mikeno, which is extinct, and Nyiragongo and Nyamuragira, which emphatically are not. They have erupted more than 70 times since the 1880s, and clouds of white vapour billowed from their cones. As night fell we sat around a fire and drank fine Congolese beer – a legacy from the DRC’s days as a Belgian colony – ate a good if basic dinner, then fell asleep in this strange, exotic land.

The magic hour – Early the next morning our rangers explained the rules for watching mountain gorillas. We could stay one hour only. We had to keep our distance and wear face masks to spare them from infection. We should avoid eye contact. No flash photography. Several groups live on Mikeno’s forested flanks. De Merode calls their survival during two decades of warfare “the greatest miracle in modern conservation”, and credits his rangers who ventured out almost daily to monitor them, with or without the rebel groups’ approval. In all, some 140 rangers lost their lives protecting the park.