It's not every day you get lowered 120 metres – 400ft – into a vast dried-out magma chamber inside an ancient volcano, suspended on a mechanical window-washing platform normally used for cleaning skyscrapers.
The BBC is hotting things up with the Volcano Live series, which starts tomorrow. But Iceland is the only place in the world to offer paying guests the chance to see what a volcano looks like on the inside, by experiencing a new adventure called, yes, "Inside the Volcano".
For this summer only, those adventurous enough can descend deep into the dried-out magma chamber of Iceland's Thrihnukagigur volcano – translated it means Three Peaks Crater. This is a dormant volcano that last erupted more than 4,000 years ago. (You can be assured that following years of detailed research, volcanologists and geologists are confident there is no risk of it erupting any time soon.)
The Thrihnukagigur volcano is located in Blafjoll Country Park, just 20km (13 miles) from Reykjavik city centre. To get to the volcano's base camp, visitors must first take a 45-minute guided walk across a huge lava bed. I crossed over dried, jagged black lava that was less friendly to walk on than the deep spongy moss growing around it.
On arrival, the guides gave us a safety talk and explained what we could expect during the next hour. Dressed like miners, in waterproof clothing, a climbing harness and a hard hat and lamp, we then hiked 400 metres up the outside of the volcano's narrow cone.
Typically, the crater of a volcano closes once the eruption ceases and the lava cools to form solid rock, making it impossible to enter. But, here, volcanologists believe the lava must have drained away via another outlet, or solidified on the walls, thus leaving the magma chamber empty.
Guide Einar Stefansson first explored the volcano with his brother 19 years ago, using climbing ropes to rappel into the deep magma chamber. The planning stages for their big idea to take small guided groups into the volcano involved years of meetings and site visits by mountain guides, climbers, construction engineers, volcanologists and geologists, whose combined skills helped make sure the whole experience would be a safe one.
"Six years ago, a National Geographic crew was making a film about volcanoes in Iceland," said Einar. "They came to us and asked if we could assist them in accessing the crater. We had done this before with a film crew, using mountain-climbing techniques to lower the crew in and out on ropes. This method was too dangerous, with guys swinging on the end of ropes. I said I'd never do it that way again, and we came up with the idea of using a support across the top of the crater and some sort of mechanical lift attached, to gain access."
Thrihnukagigur's cone sticks 35m out from the surrounding landscape. At the top is a black hole, four metres square, a funnel-shaped opening that is the only way in and out of the volcano. Above the crater is a construction crane beam, which is laid across the opening of the crater and acts as a support for the lift mechanism and walking platform.
I was attached to a safety line before I edged along a platform that looked like half a bridge. I walked out over the crater, darkness below me, then stepped on to the open lift – the mechanism that is more typically used for cleaning skyscraper windows.
Our group of five slowly descended into the cone's narrow bottleneck, bumping and scraping occasionally against colourful rock walls. At points, we pushed the lift away from outcrops that jutted out from the sides. The temperature dropped gradually as we continued our 10-minute descent.
Einar explained how a particularly unusual formation that covers the inside of the cone was formed. "As the volcano pumped out lava it dried on the inside of the cone, creating a formation that resembles a stack of pancakes, it's an impressive sight."
The project is a work in progress; this summer's opening is a trial that could lead to bigger things. Einar told me about the team's plan, a huge investment to construct a tunnel from a plateau south-east of the crater that will cut through the volcano wall to a viewing gallery, 40 metres above the magma chamber. A sturdy circular staircase structure will lead down to the chamber floor. Their project is currently being reviewed, and is subject to an environmental impact assessment. They will know later in the year whether or not their plans have been accepted.
Clear of the narrow cone, we entered a massive vault. We stopped, dangling in mid-air to take in the vast size of the chamber. Bright floodlights brought the magma chamber to life. At the sides, the chamber's edges angled down another 80m, with long, dark passages penetrating further into the Earth.
What were arteries carrying lava through the rock are now thick black lines around the chamber. Psychedelic swirls of red, pink, orange, black, green and other colourful blends covered the walls. I craned my neck and looked up to see a tiny dot of daylight at the top. We were a long way down, deep inside the volcano.
Volcano Live, hosted by Kate Humble and Iain Stewart, is broadcast on BBC2 from Monday 9 July until 12 July
Discover the World (01737 218 800, discover-the-world.co.uk) offers a three-night Superjeep Volcano Adventure itinerary, including guided 4x4 excursions from Reykjavik to Strokkur Geyser, Gullfoss waterfall, and Thingvellir National Park, plus the “Inside the Volcano” tour, from £985 per person including flights with Icelandair from Heathrow, Manchester and Glasgow, and B&B accommodation. Departures until 17 August.