Camping 200m inside an active volcano is understandably hot. Abseil 300m beyond that and you're not far away from cooking.

"It would be like running a marathon with a wetsuit on," Auckland-based Geoff Mackley explained to the Herald on Sunday this morning from a hotel in Port Vila, the capital of Vanuatu.

"It's very hot," he said. "It really saps your energy -- it's just extremely hot."

Mackley was back in Port Vila recovering after leading a week-long volcanic expedition alongside fellow Auckland explorer and photographer Bradley Ambrose and Chris Horsley from England.

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The team of three took eight paying customers from New Zealand, Australia, the United States and Canada down into the active Benbow cone on the volcanic island of Ambrym.

It was their first attempt at offering extreme expedition tourism.

The group left the Vanuatu capital last week and flew by helicopter and fixed-wing aircraft to an airstrip on Ambrym Island, a volcanic island in Malampa Province in the archipelago of Vanuatu.

A helicopter then flew the group directly inside the active crater of Benbow, where they set up camp on a floodplain 200m vertically down.

American Nik Halik poses inside the crater of the Benbow volcano on Ambrym Island. Photo / Bradley Ambrose
American Nik Halik poses inside the crater of the Benbow volcano on Ambrym Island. Photo / Bradley Ambrose

"We actually landed inside the volcano," Mackley said. "There's no real way out once you're in there. [There are] very steep cliffs, so you get dropped into the inner crater and from there we set up anchor bags."

The huge bags, filled with sand and rocks, were anchors for the ropes.

The group took turns, over seven days, abseiling 300m further down towards the lava lake.

Mackley said they went down an 80m sheer cliff, then climbed across a collection of huge boulders, abseiled further down another cliff and ended up beside the lava. This was the lowest place a person could go without injury or death by lava.

But the 51-year-old said there is not a lot that can go wrong. "If the volcano erupts, well, you're screwed, anyway."

The biggest danger, apart from an eruption, is being hit by falling rocks, he said.

One of the Americans in the group found this out the hard way.

The man was walking around in the crater when he somehow dislodged a huge boulder, Mackley said.

The group estimated the rock weighed about 500kg.

A helicopter takes off from the crater of the Benbow volcano on Ambrym Island. Photo / Bradley Ambrose
A helicopter takes off from the crater of the Benbow volcano on Ambrym Island. Photo / Bradley Ambrose

It rolled over the American and then boulder and man rolled about 20m down the hillside.

The only injury the man suffered, Mackley said, was a hole -- about 1cm in diameter -- in his leg.

After first aid he was still able to climb down to the lava lake the next day.

Mackley said once inside the Benbow cone the group were relatively sheltered.

Another active volcanic crater 2km away on Ambrym Island, which Mackley and Ambrose have descended a combined 27 times, is regularly hit by severe storms and wind.

The Marum cone sits at the very top of Ambrym and is much more exposed. It is also very deep -- 400m vertically down.

Ambrose has made 21 descents of Marum, which is the unofficial world record.

"It's a fairly daunting task for anybody who is not familiar with that sort of thing," Mackley said.

"This one [Benbow], being inside the crater, you're actually very well protected from bad weather by huge cliffs," he said.

"It's actually better."

Camp inside the crater of the Benbow volcano on Ambrym Island. Photo / Bradley Ambrose
Camp inside the crater of the Benbow volcano on Ambrym Island. Photo / Bradley Ambrose

Mackley has descended Benbow once and Ambrose has done it three times.

Mackley said the Benbow expedition was good value for money compared to other extreme tourism options offered around the world.

"You can pay US$100,000 ($149,000) to climb Mt Everest, where thousands of people have been to the top and you stand a 50 per cent chance of dying. Whereas where we go, there have been more people on the moon than have been down there.

"That's part of the allure of the whole thing."

A trip into Benbow costs at least $50,000, Mackley said, but this can be divided among all the members of the group.

Mackley's addiction to volcanic adventures and the close proximity to danger that comes with it started during the 1995-96 Mt Ruapehu eruptions.

He climbed to the top of Mt Ruapehu during those historic eruptions and, sneaking around police cordons, filmed the spectacle.

Since then he has been hooked.

"You come away from an experience like that and think, 'S***, how do I experience something like that again'."

He travelled to Vanuatu in 1997 to find out and has been back over and over again.

"We found these huge lava lakes at the bottom of this huge hole in the ground and my immediate thought was -- what would it look like to have a human down there in scale with the lava? And that has kind of been my obsession ever since."

That obsession will take Mackley and his team to the Democratic Republic of the Congo in January next year to climb Mt Nyiragongo, an active volcano inside Virunga National Park, near the town of Goma and Lake Kivu.

After the trip to the Congo with a Japanese group, they are planning another expedition to a volcano in Ethiopia.

For Mackley, it is more than simply an exciting career choice.

"It's probably a bit like a drug -- it may cause you harm, but you keep going back for more."